Polish is similar to Czech and Slovak in having words that seem to have no vowels, but in Polish at least there are invisible vowels. That’s not so obviously the case with Czech. Nevertheless, try these sentences:

Wszczebrzeszynie chrząszcz brzmi w trzcinie i Szczebrzeszyn z tego słynie.
Wyindywidualizowaliśmy się z rozentuzjazmowanego tłumu.
W Szczebrzeszynie chrząszcz brzmi w trzcinie.
I and y, s and z, je and ě alternate at the ends of some words, but the rules governing when to do this, if they exist, don’t seem sensible. The letter ť is very hard to pronounce. There are nasal vowels as in Portuguese. The ą, ć, ę, ł, ń, ó, sz, cz, dz, dź, dż sounds are hard for foreigners to make. There are sounds that it is even hard for native speakers to make as they require a lot tongue movements. A word such as szczescie is hard to Polish L2 speakers to pronounce. Polish written to spoken pronunciation makes little sense, as in English – h and ch are one sound – h, ó and u are the same sound, and u may form diphthongs where it sounds like ł, so u and ł can be the same sound in some cases.

The confusing distinction between h/ch has gone of most spoken Polish. Furthermore, there is a language committee, but like the French one, it is more concerned with preserving the history or the etymology of the word and less with spelling the word phonemically. Language committees don’t always do their jobs!

Polish orthography, while being regular, is very complex. Polish uses a Latin alphabet unlike most other Slavic languages which use a Cyrillic alphabet. The letters are: AĄ B CĆ D EĘ FGHIJK LŁ M NŃ OÓ QPRSTUVW XY ZŹŻ. Even Poles say that their orthography is very complicated.

Polish is even complex in terms of pronunciation. There are apparently rules for regarding comma use, but the rules are so complex that even native speakers can’t make sense of them.

Further, native speakers speak so fast it’s hard for non-natives to understand them. Due to the consonant-ridden nature of Polish, it is harder to pronounce than most Asian languages. Listening comprehension is made difficult by all of the sh and ch like sounds. Furthermore, since few foreigners learn Polish, Poles are not used to hearing their language mangled by second-language learners. Therefore, foreigners’ Polish will seldom be understood.

Polish grammar is said to be more difficult than Russian grammar. Polish has the following:

There are five different tenses: zaprzeszły, przeszły, teraźniejszy, przyszły prosty, and przyszły złozony.

There are seven different genders: masculine animate, masculine inanimate, feminine, and neuter in the singular and animate and inanimate in the plural. However, masculine animate and masculine inanimate and the plural genders are only distinguished in accusative. Masculine animate, masculine inanimate and neuter genders have similar declensions; only feminine gender differs significantly.

Masculine nouns have five patterns of declension, and feminine and neuter nouns have six different patterns of declension. Adjectives have two different declension patterns. Numbers have five different declension patterns: główne, porządkowe, zbiorowe, nieokreślone, and ułamkowe. There is a special pattern for nouns that are only plural.

There are seven different cases: nominative, genitive, dative, accusative, instrumental, locative, vocative. Only the genitive locative cases are irregular, the latter only in the singular. Verbs have nine different persons in their declensions: ja, ty, on, ona, ono, my, wy, oni, one. There are different conjugation patterns for men and women. There are 18 different conjugation patterns in the verb (11 main ones). There are five different polite forms: for a man, a woman, men, women and men and women combined.

There are four different participle forms, three of which inflect. Some of these are active and others are passive, but the whole system is incredibly complex. All of the participles decline like nouns, each gender adds its bit to each pattern which in turn change more according to tense.

Polish has seven cases, including the vocative which has gone out of most Slavic. The vocative is often said to be dying out, becoming less common or only used in formal situations, but the truth is that it is still commonly used.

In an informal situation, a Pole might be more like to use nominative rather than vocative:

Cześć Marek! (Nom.), rather than
Cześć Marku! (Voc.)

However, in a more formal situation, the vocative is still likely to be used:

Dzień dobry panie profesorze/doktorze! (Voc.). Dzień dobry pan profesor/doktor! (Nom.) would never be used, even in casual conversation.

Case declension is very irregular, unlike German. Polish consonant gradation is called oboczność (variation).

The genders of nouns cause the adjectives modifying them to inflect differently.

Noun
matka    mother (female gender)
ojciec   father (male gender)
dziecko  child (neuter gender)

Modifying Adjective
brzydkiugly ugly

Singular
brzydka matka     ugly mother
brzydki ojciec    ugly father
brzydkie dziecko  ugly child

Plural
brzydkie matki    ugly mothers
brzydcy ojcowie  ugly fathers
brzydkie dzieci   ugly children
Gender even effects verbs.

I ate (female speaker) Ja zjadłam
I ate (male speaker)   Ja zjadłem
There are two different forms of the verb kill depending on whether the 1st person singular and plural and 2nd person plural killers are males or females.

I killed     zabiłem/zabiłam
We killed    zabiliśmy/zabiłyśmy
They killed  zabili/zabiły
The perfective and imperfective tenses create a dense jungle of forms:

kupować - to buy

Singular  Simple Past         Imperfect
I (f.)    kupiłam             kupowałam
I (m.)    kupiłem             kupowałem
you (f.)  kupiłaś             kupowałaś
you (m.)  kupiłeś             kupowałeś
he        kupił               kupował
she       kupiła              kupowała
it        kupiło              kupowało

Plural
we (f.)   kupiłyśmy           kupowałyśmy
we (m.)   kupiliśmy           kupowaliśmy
you (f.)  kupiłyście          kupowałyście
you (m.)  kupiliście          kupowaliście
they (f.) kupiły              kupowały
they (m.) kupili              kupowali
The verb above forms an incredible 28 different forms in the perfect and imperfect past tense alone.

The existence of the perfective and imperfective verbs themselves is the least of the problem. The problem is that each verb – perfective or imperfective – is in effect a separate verb altogether, instead of just being conjugated differently.

The verb to see has two completely different verbs in Polish:

widziec
zobaczyc

Widziałem – I saw (repeatedly in the past, like I saw the sun come up every morning).
Zobaczyłem – I saw (only once; I saw the sun come up yesterday).

Some of these verbs are obviously related to each other:

robić/zrobić
czytać/przeczytać
zachowywać/zachować
jeść/zjeść

But others are very different:

mówić/powiedzieć
widzieć/zobaczyć
kłaść/położyć

This is not a tense difference – the very verbs themselves are different! So for every verb in the language, you effectively have to learn two different verbs. The irregular forms may date from archaic Polish.

In addition, the future perfect and future imperfect often conjugate completely differently, though the past forms usually conjugate in the same way – note the -em endings above. There is no present perfect as in English, since in Polish the action must be completed, and you can’t be doing something at this precise moment and at the same time have just finished doing it. 95% of verbs have these maddening dual forms, but for 5% of verbs that lack a perfective version, you only have one form.

It’s often said that one of the advantages of Polish is that there are only three tenses, but this is not really case, as there are at least eight tenses:

Indicative         grac       to play
Present            gram       I play
Past               gralem     I played
Conditional        gralbym    I would play
Future             będę grać  I will play
Continuous future  będę grał  I will be playing
Perfective future  bogram     I will have played*
Perf. conditional  pogralbym  I would have played

*Implies you will finish the action
There is also an aspectual distinction made when referring to the past. Different forms are used based on whether or not the action has been completed.

Whereas in English we use one word for go no matter what mode of transportation we are using to get from one place to another, in Polish, you use different verbs if you are going by foot, by car, by plane, by boat or by other means of transportation.

In addition, there is an animate-inanimate distinction in gender. Look at the following nouns:

hat      kapelusz
computer komputer
dog          pies
student    uczen
All are masculine gender, but computer and hat are inanimate, and student and dog are animate, so they inflect differently.

I see a new hat – Widze nowy kapelusz
I see a new student – Widze nowego ucznia

Notice how the now- form changed.

In addition to completely irregular verbs, there are also irregular nouns in Polish:

człowiek -> ludzie

Let us look at pronouns. English has one word for the genitive case of the 1st person singular – my. In Polish, depending on the context, you can have the following 11 forms, and actually there are even more than 11:

mój
moje
moja
moją
mojego
mojemu
mojej
moim
moi
moich
moimi

Numerals can be complex. English has one word for the number 2 – two. Polish has 21 words for two, and  all of them are in common use.

dwa (nominative non-masculine personal male and neuter and non-masculine personal accusative)
dwaj (masculine personal nominative)
dwie (nominative and accusative female)
dwóch (genitive, locative and masculine personal accusative)
dwom (dative)
dwóm (dative)
dwu (alternative version sometimes used for instrumental, genitive, locative and dative)
dwoma (masculine instrumental)
dwiema (female instrumental)
dwoje (collective, nominative + accusative)
dwojga (collective, genitive)
dwojgu (collective, dative + locative)
dwójka (noun, nominative)
dwójkę (noun, accusative)
dwójki (noun, genitive)
dwójce (noun, dative and locative)
dwójką (noun, instrumental)
dwójko (vocative)
dwojgiem (collective, instrumental)
dwójkach
dwójek
dwója
dwójkami

Polish also has the paucal form like Serbo-Croatian. It is the remains of the old dual. The paucal applies to impersonal masculine, feminine and neuter nouns but not to personal masculine nouns.

Personal Masculine

one boy     jeden chłopiec
two boys    dwóch chłopców
three boys  trzech chłopców
four boys   czterech chłopców
five boys   pięciu chłopców
six boys    sześciu chłopców
seven boys  siedmiu chłopców
eight boys  ośmiu chłopców

Impersonal Masculine

one dog     jeden pies
two dogs    dwa psy
three dogs  trzy psy
four dogs   cztery psy
five dogs   pięć psów
six dogs    sześć psów
seven dogs  siedem psów
eight dogs  osiem psów
In the above, two, three and four dogs is in the paucal (psy), while two, three or four men is not and is instead in the plural (chłopców)

A single noun can change in many ways and take many different forms. Compare przyjaciel – friend

                             Singular         Plural
who is my friend             przyjaciel       przyjaciele
who is not my friend         przyjaciela      przyjaciół
friend who I give s.t. to    przyjacielowi    przyjaciołom
friend who I see             przyjaciela      przyjaciół
friend who I go with         z przyajcielem   z przyjaciółmi
friend who I dream of        o przyjacielu    o przyjaciołach
Oh my friend!                Przyajcielu!     Przyjaciele!
There are 12 different forms of the noun friend above.

Plurals change based on number. In English, the plural of telephone is telephones, whether you have two or 1,000 of them. In Polish, you use different words depending on how many telephones you have:

two, three or four telefony, but
five telefonów.

Sometimes, this radically changes the word, as in hands:

four ręce, but
five rąk.

There are also irregular diminutives such as

psiaczek  -> słoneczko

Polish seems like Lithuanian in the sense that almost every grammatical form seems to inflect in some way or other. Even conjunctions inflect in Polish.

In addition, like Serbo-Croatian, Polish can use multiple negation in a sentence. You can use up to five negatives in a perfectly grammatical sentence:

Nikt nikomu nigdy nic nie powiedział.
Nobody ever said anything to anyone.

Like Russian, there are multiple different ways to say the same thing in Polish. However, the meaning changes subtly with these different word combinations, so you are not exactly saying the same thing with each change or word order. Nevertheless, this mess does not seem to be something that would be transparent to the Polish learner.

In English, you can say Ann has a cat, but you can’t mix the words up and mean the same thing. In Polish you can say Ann has a cat five different ways:

Ania ma kota.
Kota ma Ania.
Ma Ania kota.
Kota Ania ma.
Ma kota Ania.

The first one is the most common, but the other four can certainly be used. The truth that while the general meaning is the same in each sentence, the deep meaning changes with each sentence having a slightly different nuanced interpretation.

In addition, Polish has a wide variety of dialects, and a huge vocabulary. Although Polish grammar is said to be irregular, this is probably not true. It only gives the appearance of being irregular as there are so many different rules, but there is a method to the madness underneath it all. The rules themselves are so complex and numerous that it is hard to figure them all out.

Polish appears to be more difficult than Russian. For example, in Russian as in English, the 1st through 3rd person past tense forms are equivalent, whereas in Polish, they are each different:

          English   Russian     Polish

1st past  I went    ya pashou   ja poszedłem
2nd past  you went  ty pashou   ty poszedłeś
3rd past  he went   on pashou   on poszedł
Even adult Poles make a lot of mistakes in speaking and writing Polish properly. However, most Poles are quite proud of their difficult language (though a few hate it) and even take pride in its difficult nature.

On the positive side, in Polish, the stress is fixed, there are no short or long vowels nor is there any vowel harmony, there are no tones and it uses a Latin alphabet.

Polish is one of the most difficult of the Slavic languages. Even Poles say it is very hard to learn. Most Poles do not learn to speak proper Polish until they are 16 years old! Although most Poles know how to speak proper Polish, they often use improper forms when speaking formally, not because they do not know how to speak correctly but simply because they feel like it.do

It is harder than Russian and probably also harder than Czech, though this is controversial. There is a lot of controversy regarding which is harder, Czech or Polish.