This is a thing I wish more people understood. We're not here to whine on the internet. The whole point of an Alpha release is to air out these things so that Larian can get ahead of problems. If we didn't see a great game just under the surface of this one, then we'd have just stayed quiet, gotten a return from steam, and left.
A large portion of the flaws and broken mechanics in BG3 stem directly from the deviations away from the rules of 5e. When you have a system that is designed to act in a certain way, every change has knock on effects.
There is no option to use the perception or investigation skill actively, instead your "passive" perception is a roll. This causes several problems and exploits. First, because it's a roll, it tells you that there is something to notice, but without a way to investigate, you can't move carefully through a trap filled dungeon the way you would in normal D&D. But also, your familiars get a "passive" perception check, and since each summoned familiar is a new creature, and is treated like a disposable pet, it can be summoned infinitely for free. So any time your group fails a perception check, you can summon new familiars until one succeeds on the check. If passive perception instead worked the way it was supposed to, then this exploit wouldn't exist. Instead, any character that had a high enough passive would automatically notice the thing on the ground.
Without active perception, there is nothing that the AI can do once your party successfully gets into stealth. Because Passive perception doesn't exist, everyone automatically succeeds on stealth checks once they get out of line of sight. Stealth is supposed to be something you can attempt with cover or concealment, but there is no cover or concealment mechanically, only line of sight. This means that rogues get shafted again, since they need total concealment to make a stealth check. The changes to cover and concealment and the seeming replacement with advantage and disadvantage from elevation also play havoc with balance. Cover is supposed to give a bonus to AC, and it's supposed to let you hide. It's not supposed to give you a bonus to hit.
The AI will drop everything to get a height advantage so that it can more easily hit you. And there is no benefit to being partially behind something. These two things trivialize a lot of the tactics of a normal 5e fight. But surface effects just annihilate them. Having rare environmental advantages and disadvantages exist in a game adds some fun flavor to fights. Having nearly every fight devolve into a fight to see who can explode the other the most with random explosive barrels does not. But it's worse than that. That's an easy fix, have less barrels, give the goblins fewer flasks of acid. Cantrips however are another can of worms.
The funny thing is – DOS2 already had what you would describe as Passive Perception with their Wits ability. You needed a certain number in Wits and you’d automatically succeed as noticing things. So they’ve moved away from something which is more in tune with 5E toward some broken mechanic that ruins the experience. I really don’t think they understand D&D very well.
Feel free to steal my profile pic if you feel the same way. Let's show some solidarity.