I think there are a lot of people having very different gameplay experiences due to the randomness and apparent instability of the AI.
My campaign playthrough has actually been pretty tolerable, though the Aliens can get crowded or hung up and definitely show some weak programming.
You can tell they didn't want console thumbstickers to feel overwhelmed by a nimble Alien, even though they do use the walls and ceiling, on occasion.
It's strange, it's almost as if the Alien AI suffers from the same caveats surrounding the level architecture that the friendly AI does, like there just isn't enough room or the swarm isn't properly spawned in that part of the level.
Just make one of the patches the AI Director, add acid damage, and you're set.
But what are we gonna do about that level 2? God, forever. Takes bloody forever.
