Ultimately, in my reading, he was a good guy. He gets sent off to try and convince Dooku that's he's turned to the dark side, but the story goes kind of back and forth about whether he actually went over to the dark side, or if he's really a double agent for Dooku. Ultimately he ends up on Kashyyyk when he's nearly killed by O66. He manages to escape the troops trying to kill him, and even fights the Clone Commander personally tasked with killing him. He manages to escape and eventually meets up with his girlfriend/wife (I can't recall if they marry) and they have a son together.
As far as the war goes, he doesn't get involved in a lot of the front line fighting like Kenobi and Skywalker. He does a lot of spying stuff. He commands some troops, but ultimately doesn't like or trust the clones.