In my initial evaluation of Lewis, I graded him down (slightly!) for being a DE/OLB "tweener."
Since then, I have remembered that the Lions run the wide nine and might be absolute geniuses for this pick, which was already a great value in the fourth round. Defensive ends in the wide nine tend to have a lot in common with 3-4 rush linebackers, except that they very rarely have to do anything other than rush the passer.
If that's how the Lions see Lewis, then they might have a guy with the perfect frame, but they do need to work on his pass-rush technique. Lewis doesn't have the most explosive first step off the line, but the wide nine compensates for that a bit by giving guys a better rush angle and a head of steam getting into the line.
Of course, this is all conjecture for the future. I don't see a great chance of Lewis breaking the Lions defensive rotation this year, on the line or at linebacker. What I do see is him figuring out what his role is in that defense, learning it and refining his ability there for 2013.
I also see him being a terror on special teams, as perhaps the heir apparent to the "Pain Train," Zack Follett, only with more long-term defensive skills. As Jim Schwartz said, he's expected to play "the hammer position."
If you doubt me, play the video to see the pops he put on Stanford in the 2010 Brut Sun Bowl. His long-term potential is far greater than special teams, but he'll be okay on special teams in the meantime.
And if you pay close attention, one of the great things is that while Lewis is laying big hits, they're legal, clean hits right in the numbers. Nothing he'll get flagged or fined for at the NFL level.
He's the right kind of mean, and it's beautiful.