for example level 1 and 2 is in sewers.Walls are red and tunnel is square.It looks ok but tbh i think real sewers should be round like pipe(it can cause problems in grimrock because normal dungeon square got floor ,roof and 2-4 walls , in this case you would have only 2 walls and no floor or roof).
About monsters - modeling them takes a lot of time and efforts

I am including image of my tries ,kobold(cut in half) ,rust monster and some walls .Rust and walls got no zbrush details
http://img861.imageshack.us/img861/8287/eobmr.jpg