The Lion and the Broncos are my two sleeper teams this season.
Some say the Lions are good enough to make it to the Super Bowl. I don't know if I would go that far, just need to see it for myself. But they certainly look good enough to make it to the playoffs.
As for the Broncos, they look much better than a 4 win team they were last year. Kyle Orton is a stud. He may not be in the Brady/Manning/Bress/Rogers/Rives class, but he's certainly in the second tier class. Also, Elvis Dumervil and Von Miller are unblockable. The Broncos could have one of the best pass-rushing defenses in the NFL.
Detroit has never been good and Detroit will never be good. The greatest RB in history (Barry Sanders) couldn't save that franchise.