Ok, I should actually talk about stuff that I do think is wrong in 5e.
Probably my two biggest gripes are clerics and druids. Note, this is 100% just a personal thing and I know that I'm in the minority here.
1. Clerics don't know what they are supposed to be. Unless you're a war priest or something else that gets martial weapons, your cleric's cantrips are far, far better than any weapon attack you can make. There's just no real reason to use a weapon. Your cantrips will deal more damage and hit more often than any attack you make AND if you don't use weapons, you don't need to worry so much about MAD.
But, then, you've got the best armor proficiencies in the game outside of fighters. Your cleric most likely has the best AC in the game, and quite probably second best (or even best) HP in the group. But, you're better off standing in the back line pew pewing away with cantrips.
It drives me mental that clerics should be the second string or even first string tank in the group, but, if you do, then you're getting smacked fairly often, losing concentration and your weapon attacks are very, very bad.
I really think that there should be a cleric cantrip that allows a weapon attack as part of the cantrip and deals cantrip damage (d6/5 levels? something like that) on top of the weapon's damage. The cleric won't be a damage dealing star, but, at least then there'd be a reason to stand in the front line.
2. Druids bug me too. Now, I've never played a Moon Druid, nor seen one played, so, maybe that's the issue. But, I have seen a few played and played one myself for quite a while and to me, druids are just wizards with a specialized spell list. You're chucking Produce Flames every round, so, not particularly different from the wizard chucking fire bolt. Depending on which type of druid you are, you may very well be getting iconic wizard spells like invisibility or fireball as part of your spell list. AND, for some reason, druids are the summoning class while actual Conjuration wizards can't actually summon monsters.
I really, really don't like the 5e druid. I think it's too much wizard and not enough actual druid. A druid shouldn't be dropping fireballs on enemies and I hate that druids mugged conjuration from wizards. I do know that once I simply adjusted my point of view about my own druid and just started calling him a Conjurer, I was much happier.