He's really interesting to watch. His big pitch is a very hard sinker, which he uses to induce ground balls. He doesn't strike a lot of people out, so a lot of balls are put into play. From what I've seen so far, that's a double-edged sword--because so many balls get put into play, he ends up giving up a lot of weird hits (infield singles, ground balls that find a hole in the infield defense, plays that make the defense help him out...) However, he also gets out of a lot of jams by getting lots of DPs.
When things are going well, he throws 10 pitches, gets 3 ground balls to his infielders, and heads back to the dugout. When he doesn't get the breaks, those ground balls turn into hits and runs. Take the third inning of Sunday night's game for example (the only inning in which the Tigers scored). With runners on first and third and one out, Carmona jammed Sheffield and got him to a hit a ground ball--however, it was hit hard enough up the middle that all Peralta could do was dive, knock it down, and keep it in the infield. Sheff was safe on the infield hit and both runners advanced. Carmona then made a nice pitch to Ordonez to induce a tailor-made inning-ending double play. However, the ball found a whole between 3B and SS, another runner scored, and the inning continued. Carmona got the next two batters to get out of it, but that's how it goes. If those ground balls find holes, he'll be in trouble. However, when they get hit to fielders, he'll be very efficient and effective.
The thing I like about Carmona is that he seems to play with confidence and his sinker should be a consistent out-pitch for him. I think he's for real.