From a ""COMPETITIVE"" standpoint (mostly duel issues, but other game modes apply)

1: I am open to the idea of champions and abilities. things dont need to be "quake 3 again" forever. I am not ok with "instant full heal" "turn invisible and invulnerable" "see through walls" "80 damage (50 of it is a DoT) projectile spam" "Pocket quad damage every 30 seconds" etc. as the abilities are too strong and out of place. You can't just take a game not designed around them and throw them in, and that's exactly what happened here. It's this weird inbetween of a hero shooter and arena shooter. Not as unplayable as LawBreakers, but still not very good. Balance issues all over the place, asymmetry up the ass, instant kills from 150 damage charge that has a hitbox 3x as wide as my character collision (literally killing people through walls by running into the wall), clutch vs clutch shield stalemates, nyx vs nyx ghostwalk stalemates (i can link you dooi vs chance 9x overtime 45 minutes on one map duel if you want examples)

2: Shitty bugs (yes I know it's beta) that keep coming back, patches that fix them, while the next patch re-introduces the bug that was fixed, map collision issues up the wah-zoo to the point of people standing under the map and shooting people above it, etc, etc, etc...

3: (kind of acceptable): no forcemodel, no picmip, difficult to see enemies especially certain skins on certain maps; visibility issues in general, and the shittiest workaround ever created by having a stupid:small_red_triangle_down:  above their head showing that there's an enemy there...really really bad solution for an aFPS.

4:  Weapons are imbalanced. LG does 7 in this game, but stacks are like 1/2 as big as they are in QL, where it does 6. It has no pushback, but that doesn't matter because you can just move faster than the guy you're chasing with it. Railgun doing 80 is also way too much when characters die in 2-3 railgun shots at maximum armor/health stack instead of 4-5. Rockets move too fast and the projectile is too small. No grenade launcher is a real issue especially for defensive play. No, the Tribolt does not replace the functionality. This is an entire argument itself.

5: Armor and megahealth are too weak. When maximum stack (INCLUDING OVERCHARGE)  is something like 125/75 for a fast character, or 200/150 for a slow fat character with a hitbox the size of a barn, these items are not useful enough. If you're at full health in any other game, the megaarmor (red armor) will give you +100 bringing you to 200, and the megahealth will give you +100 bringing you to 200.  In QC, your max is something like 75, then mega gives you 125, or your max is 150, and mega gives you 200. This is problematic because railgun does 80 damage. Previously if you pick up armor, and take a rail, you're still "ahead" a net +30 health or armor. Now, you're BEHIND a net -20. So you can only pick up armor when you won't get hit AT ALL or else it's not worth it, which leads to...

6: Armor and Mega Health timing (both at 30 seconds) makes it too hard to break control. If the player in control can time one item, he can time them all, and collect them all. In previous games, the staggered 25 sec and 35 sec respawn rates forced alternate routes instead of just using one optimal armor cycling route. For example, if I take path A, I can take red armor at 0:05 and be at megahealth in 4 seconds - I grab it at 0:09. In QC I do this every time, with no issue, repeatedly, the whole fucking round. 0:35, 0:39, 1:05, 1:09, etc etc.
In QL, taking the same route on the same map (since they're both based on quake 3 physics), if I grab both items at 0:05 and 0:09, armor is sat 0:30, and megahealth is at 0:44... and then the next spawn, it'll be 0:55, and 1:19...so this might not be the optimal path, as I'd get there super early, and be sitting in a disadvantageous position waiting for spawn...So it would eventually force me to take megahealth instead of the armor first, OR MAYBE even delay the item spawning (let it sit there for 5 seconds and not pick it up) to help line it up so it suits me more for the next spawn, OR MAYBE if I don't alter the natural spawn rate a little bit, they'll eventually spawn at the same time, giving the player who does not have control more of a chance to come back. I can't be in two places at once, and I'd have to chose red armor or megahealth, or try to force an engagement/ambush/fight so he can't collect the one he's going for, then go get the other one after.

6a: I also could write a big essay about why having "one red, two yellows" is better than "one mega armor, and like 3-4 smaller armors that respawn every 15 seconds and fill a heart container"

6b: health/armor "containers" are probably the worst design flaw, getting +13 from something that could give you +24 or +35 (because it rounds) is really stupid (examples are picking up a health globe with 12 health brings you to 25, picking up the same globe from 1 health brings you to 25, but if you have 15 health, it brings you to 50)

7: Duel mode is absolutely skill-less. When there's only 3 frags, your first spawn matters a LOT, and with only 5 minute rounds (before sudden death), there's a lot less time to break control from the player who got the better spawn (which, if you read 6, you'll understand it is much harder to break item control in QC than QL, so considering you're given even LESS time to do it, well, sucks to be you if you got a bad spawn!). Speaking of bad spawns, even one bad spawn can really ruin the round, even if it isn't your first one. There's a lot more I could say about this, but I think that's enough without linking videos of people dying, and then spawning in the same spot to die again 0.26 seconds later.

8: Maps are too open, even the "old school" maps have been modified to be even more open and wide, making rail even stronger. I can show you exact examples of this, but it just continues down the "all aim, no brain" design philosophy of the game, which really weakens it from a strategic or depth perspective, and basically is "quake for counterstrike players" because you can be carried by your aim. Especially on maps like corrupted keep where defensive, predictive "brain play" is almost impossible (no railgun, no real spots to set up ambushes, it's very small and very circular/connected, so there's no room to force a long-range engagement, or land a rail and duck behind something to re-engage later)

8a: Note: I presonally am a more aggressive player, so this actually works out better for me; but I realize it's worse for the game as a whole because it forces one-dimensional play, something that was not an issue in previous quakes. I am not saying I want people to be able to sit in a corner camping with railgun, but they shouldn't be forced to just +forward with lightning gun either, because the map might as well be "final destination fox only" or something.

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from a casual standpoint:

1: no CA (it's been confirmed), no freezetag (might be in a "weekly tavern brawl" kind of thing), no ctf (ok, it's coming apparently, because of how many people hate sacrifice)

2: Ignoring all the lootbox trash and blue haired marketing ploy rule 34 bait, cosmetics are kind of lackluster and the only "good" ones are just skins from previous games...people want cool fun interesting cosmetics, not "moving the knee pad from Ranger's left leg to his right" (the doomguy fan service is a good example, but again, it's just the classic suit from doom1+2

3: only like 6 fucking maps, sacrifice, duel, ffa, tdm all on the same fucking maps (double edged sword; easier for people to learn them, also much easier for people to get bored of them)

4: most of the gameplay (for better or for worse) is the same as quake 3 arena on the surface

5: most weapons feel very low impact (sound and graphically), as well as cringy designs (flipping tables, heroin addict slash and anarki, edgelord chars like ranger, shitty voicelines and bad characters ruin games like this, just look at lawbreakers)

6: all weapons "feel" bad - especially rocket launcher. It feels better than previous patches because the projectiles display client side. But that's all that was changed. They're still registered server side, with the same ~200ms delay that they had before, so, that's why lots of people get these "direct rocket does 0 damage" issues - because what is shown on your screen, at 0ms, isn't really what happened, at 250ms (input lag, actual network latency, and the stupid quake champions patented rocket delay)
Personally I'd rather see what's actually happening, but they changed it for the "perception" that it's fixed. Very shady and shitty.

7: they're charging $30, when I can buy pubg, overwatch, lawbreakers (yecch), rainbow 6 siege, titanfall2, etc, all for the same price or less

8: you can unlock characters permanently, but only from reliquaries (random drops) that you can only earn from leveling up or spending money on them (They are the "premium" lootbox, as opposed to the backpacks that you normally get)

8a: it is not evident to the average f2p player that you can unlock characters permanently, as the only option in the store is to "rent for 24 hours" a champion (now, it's a relatively nominal amount of favor, like, one daily quest and 1-2 matches will get you a champion, but most people don't want to "grind out" 3 matches before they can play the character they want to)

9: duel is STILL too hard to get into, despite the dumbed down casual version they are trying to push.

10: public sacrifice with no coordination is quite possibly the worst public game mode I've ever played in an FPS, as it is not clear to anyone (still, like, 5+ months after the first beta) that once points are determined, you can't capture the other team's home base, you can only score by bringing the soul back to your own

sacrifice game mode itself gets its own rant
duel game mode itself gets its own rant
but those are the main issues that affect everything
did i mention they're asking people to pay $30 to play a game that doesn't have clan arena, the most played game mode in every arena fps ever?
despite it being so casual, I think QC needs it to survive.