Detroit has a good enough running back. They need offensive lineman to protect the QB and keep holes open for Stewart to run through. I haven't seen enough of McMahon to know if he is a starting QB, but he is a start in the right direction. I would dump Charlie Batch and sign Trent Dilfer. Before you laugh, realize Dilfer has won a superbowl and is a winner. He is not a Brett Favre, but if you put good weapons and o-line in front of him, he can be a serviceable QB until McMahon matures in a year or two. Their second leading receiver is their fullback, never a good thing. Upgrade the WR core, Morton is a keeper and Emanuel a decent third down guy, and Crowell might get better if they have better QB play. Sloan is a serviceable TE, but they need more catches out of the position to take the heat off of the QB and WRs.
They have good LBs in Greene and Claiborne. Need another CB, Westbrook is overrated and doesn't get enough picks. Plus they need someone that can rush the passer besides Porcher, who is 32 (33?).
Basically it is going to take 2-3 years to get this team back in playoff contention.