me answering wotc on their survey

True Strike, Witch Bolt, Blade Ward, Find Traps, Weird, Mordekainen's Sword, and Enthrall are either so niche that it's never worth taking or useless in every situation it can apply to.

Polymorph is the strongest all-around spell in the game capable of "healing" allies by giving them a new HP bar, debuffing enemies by turning them into critters, gives movement utility by turning into a flying/burrowing/swimming beast, and even helps scouting by letting one turn into a small, inconspicuous beast. Most spells have a specific use that they're made for and perform very well, but Polymorph is able to apply to a multitude of situations to at least decent effect.

I understand Fireball is stronger than it should be as a 3rd level spell because its iconic, but  it's become a must have and after a couple years of spellcasters giggling about how excited they are to pick up fireball the moment they hit level 5 it's annoying to think about now. Every situation that doesn't care about collateral damage's first solution has become fireball! Fireball! What if I Fireball them? I'm sick of it. The spell's too strong.

Healing Spirit is broken, it can't be debated. 10d6 hp restored for EVERY creature that runs through it out of combat? Compare it to what was previously the dedicated out of combat healing spell, Prayer of Healing that heals 2d8+Spellcasting Mod for only 6 creatures. Not to mention that Healing Spirit only takes 1 minute compared to Prayer of Healing's 10 minute cast time. Who was responsible for this? Who thought this was a good idea? Even Crawford's Sage Advice ruling of giving Healing Spirit 2xSpellcasting Mod charges before it runs out doesn't entirely solve the problem. It's still 10d6 healing out of combat in just a minute, albeit not for everyone but still a good hefty chunk for anyone that took a bit of damage after an encounter.

Forcecage is just... there. Cast Forcecage on somebody. If they don't have some sort of teleportation or planar travel means to even /try/ to escape, they're locked in. No save, no way to resist. That's it. You're locked in the timeout corner for an hour and it doesn't even take concentration. Maze is an 8th level spell that only lasts 10 minutes, requires concentration, and lets someone try to escape every turn as an action. Why is Forcecage better in every aspect?

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There aren't any /overpowered/ feats necessarily. It's just that there's a vast majority of feats that are either flat out garbage or too situational to pick over the actually good ones.

Let's stick to the PHB for this one. Crossbow Expert, Great Weapon Master, Sharpshooter, War Caster, Resilient, Magic Initiate, and Polearm Master. These are the good feats. The ones that are optimal to pick up if it fits your build. They aren't overpowered by any means. It's just that a feat means forgoing an Ability Score Increase, and that's a very important choice. These feats are the only ones that its worth making that choice for without a second thought.

Everything else is either okay, fit only for specific niche gimmick builds, or absolutely horrendous.

Lucky, Actor, Alert, Tough, Inspiring Leader, Dungeon Delver, Ritual Caster, Sentinel, Mobile, Healer, Mounted Combatant, and recently Shield Master after Crawford retconned his own ruling concerning the bonus action shove. These are okay feats, not terrible, but generally not worth taking over the Ability Score Increase when optimizing, but I don't have any problem with them.

Athlete, Charger, Defensive Duelist, Dual Wielder, Durable, Elemental Adept, Grappler, Heavily Armored, Heavy Armor Master, Keen Mind, Lightly Armored, Linguist, Mage Slayer, Martial Adept, Medium Armor Master, Moderately Armored, Observant, Savage Attacker, Skilled, Skulker, Spell Sniper, Tavern Brawler, and Weapon Master. These are garbage. Awful feats that don't deserve to ever be taken over a different option unless someone is purposely gimping themself.

Feats are by no means free. Taking a feat in the first place is a choice that means missing out on +2 to one stat or +1 to two. And to miss out on that means that you need something just as good. The vast majority of feats in the PHB are not worth making that choice.