We all like Larian here, at least to some extent. Otherwise we wouldn't have bothered to pay full price for a severely unfinished EA game, play the buggy mess, create an account in their forums and take time out of our days to come and try to better the game. Still, it remains the fact that Larian has taken several liberties with the game which made many people upset, and rightly so...
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.
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.
Supposedly the reason for the higher health on all of the monsters is to balance out the lower AC that they were given to make fights more "fun". I think that that's a justification that was given, but I think the real culprit behind the decision is Fire Bolt. On a miss, Firebolt can do something like 3d4 damage before the targeted creature gets to act. On a normal health goblin, this has a decent chance of killing it outright. Because of the ease of applying status effects anywhere at any time, with no downside, low health enemies would have no chance of surviving a party of firebolting Wizards who kite as they ignite. But if you cite "fun"you can justify a lot of back end changes to cover up an unbalanced mechanic. Never mind the damage that said change caused to things like sacred flame, who don't get the same buff to hit, and now has to chew through more health to boot.
Of course if the hypothetical Fire Bolt Brigade got tied up in melee, they'd still have some trouble, because they'd have to waste their action trying to disengage so that they don't light themselves on fire. Except that every class has taken some levels in rogue, and thus can disengage as a bonus action. But worse, disengage is tied to jump, so you don't even need to make a check to pass through or over an enemy square. This means that clever positioning to box someone in doesn't work. Which means that Tanks can't effectively protect the squishies. It means that there is no downside to playing pure ranged and ignoring melee entirely.
But even if you are playing a Melee character, you can still get advantage if you can backstab someone. Introducing Facing is certainly a choice. It means that anyone can get advantage without the help of a flanker. Which means that there is no benefit to formation fighting at all. It throws teamwork out the window, in favour of cheesing the fact that the game is turn based. One of the conceits of the initiative system is that the round happens more or less simultaneously, which means that some actions are assumed to be possible even when it's not your turn. It's where opportunity attacks come from. But the other thing that is assumed is that you can turn to face your opponent. This is why flanking is flanking, and not getting behind someone. Instead you can walk, or jump behind someone to get free advantage on every attack.
All in all the changes that have been made reduce a party's reliance on each other, reduce the tactical nuance of the game, and make non-attack based combat more powerful than anything that any character could do.