I think Lewis is going to surprise some people. Take a look at his numbers from last season:
12 games, 58 catches, 741 yards, 10 TDs
Average those numbers out over 16 games and you get 77 catches for 988 yards and 13 TDs. Obviously he's unlikely to ever sniff those numbers at the professional level, but he was an extremely prolific college player. His production dwarfs that of recent guys like Jeremy Shockey, Heath Miller, and Kellen Winslow.
A lot of people compare Vernon Davis to Antonio Gates. While they may have some similarities in their ability to run after the catch, I'd argue that Lewis is in fact closer to Gates than Davis is. Lewis is a dangerous red zone weapon who acts like a power forward down near the goal line. He may never have elite yardage totals, but I expect him to eventually become one of top 4-8 FF TEs. He should score a lot of TDs.
I love the value that he offers in initial dynasty drafts, as I think his value is almost guaranteed to go up, possibly by as much as four or five rounds in twelve team leagues.
On the downside, his long build may expose him to a greater risk of injury and no one will ever confuse him for Anquan Boldin in the open field.