A lot went down that bugged me, from plot points that never went anywhere and the antagonists becoming cartoon villains with improbable setups (an elaborate room whose only function seems to be to be a big fuck you to the PC) to asinine, dumb gameplay design (only way to progress is to trigger a flag by inspecting a specific fluff/background element in a room full of them). Also the monsters you see were pathetic and not at all threatening, despite them apparently being able to rip armed people to shreds.
Ok, that's ringing a bell now. Yeah, I was let down that there was no greater plan the antagonist had, and the progress trigger you mention, yeah, I dealt with that as well and it pissed me off. As for the monsters, meh, I guess I assumed they attacked en masse? I didn't really think about it much, it's like wondering how Raccoon City got taken over by shambling zombies, lol, but I'm sure your point is correct.
I'm trying to think of another, comparable game but I'm failing. The last adventure game I enjoyed was Spirits of Xanadu but I can't recommend it without some serious caveats, and even then not at the full asking price of 10$ (I got it for 5$ on sale).