Agree, Omega. If he gets out in the clear he can really run. But those long legs take a while to get going.
If Dallas had a mediocre OL, I'd have more reservations about Henry. But running behind the Dallas OL, Henry would find enough room to get to the second level often enough to worry the crap out of defenses. Henry is the finisher that DeMarco Murray wasn't.
For what it is worth, Henry's 40 is faster than those of Mark Ingram, Trent Richardson, Eddie Lacy, and T. J. Yeldon.
There are no character concerns with Henry. He is focused, highly coachable, and a consistent hard worker. Saban love him.
Elliott is a safer bet and likely will be better, but there are those who want to use the 4th overall pick to add a good player to a bad defense instead of building the best running game in the NFL.
Also, Ron Dayne is not the same player as Henry -- they are built differently and their games are different. Henry is 5 inches taller than Dayne, but weighs less. Dayne fought major weight issues throughout his career. Dayne was a 270 lb. RB in high school. Dayne's weight angered Fassel; Dayne once lost 40 lbs to impress Coughlin.