I totally understand where you're coming from, and I was apprehensive too, but trust me, it's all cool. Very fucked up, very dark, funny film. Not some slushy schwimmer crap like you'd expect. Schwimmer of course plays the nice guy who gets pulled into this whole fucked up murder and blackmail plot gone wrong, but he's good in it....gets slightly more insane towards the end, and he's a good contrast against Simon Pegg's amoral maniac conman. It's one of those films that I still enjoy even though I've seen it a gazillion times. Great performances, and plot twist after plot twist right to the end make it a really enjoyable movie.
I thought Schwimmer was pretty good in Band of Brothers too. Which incidentally where he and Simon Pegg met and decided to work together on Big Nothing.