Nobody can deny that Cassel is a risky addition. He's only seen significant playing time in 1 season, and he had the services of Randy Moss and Wes Welker along with a great coaching staff helping him along the way, not to mention backing up the best QB in the league for 3 years. He's also shown a tendency to hold onto the ball for way too long because he was sacked more than any other QB.
With the bad comes the good. He's very accurate, both in the pocket and on the run, good mobility and ability to hit receivers deep. He also seems to be very durable.
I'm skeptical to sign him to a big contract before next season, but I can't wait to see how he does.