I had the same problems. Try updating to the newest version of the catalyst drivers
Im stuck on that second mission, I get to a cylinder shaped room, with bolts of electricity surging below me. Theres a hook on the ceiling, and apparently im supposed to do something with it, I couldnt figure anything out, and jumping up to the hook resulted in my death :/I got stuck there for a while. I'll give you a small clue, "use one of your item"
I thought it was fun until I tried messing with the options. When I jumped the res up to 1024x768 I ran into the problems Dan is talking about. Things got worse when I tried to reset everything to default... the textures became dark and blurry, and the mouse control problems didn't go away either.
I noticed it's coming out for consoles too... after it's released I'll give it a shot on my Xbox, but I won't bother with the PC version if the same problems are there.