Yeah, that's another thing I dislike, it's difficult to get a handle on which enemies will be alerted to gunfire relative to my position. It seems like sometimes enemies in a closed off room won't hear, and at other times every enemy on the map will start rushing me. Annoying because it hinders play style, I just always melee or throw weapons just to be safe.
Between that, the enemies sometimes going through walls as you mentioned, and the finicky lock on, a lot of the time it just seems like an exercise in complete randomness. I get the whole recklessness/don't be discouraged by dying dynamic, but I feel like I get by more on luck/fumbling through than by getting better. I don't know, maybe in a way it all makes more authentic, like it really is a bugged out, crude, and amateurishly coded 8/16 bit game. I'll probably come back to this game, but in general, I'm disappointed by the restart happy/trial and error style of the game.