The chair problem meph referenced affects more than just chairs, it's a problem with the level development staff placing images in a level and not "shaping" it with script if it's a blocked image.
Luckily it's easy to fix (depending how many different images they used though it could take a little while to fix)
The enemies i've heard are designed to be that hard so players want to move in "gangs" for survival.
Personally, i think that's over the top- i managed to kill one when i was playing the other night and it basically instantly respawned a few tiles away and aggro'd on me.
Not fun
Also: giant beavers.