Chip Kelly's offense isn't a gimmick, but I would say that it's rather one dimensional. Kelly isn't doing anything ground breaking, they are concepts that have been used in the NFL for quite sometime, what is different is the tempo, and implementation of these concepts. Peyton Manning is a fan of the no-huddle offense, the difference is he doesn't run 75+ plays a game.
The problem with Chip Kelly's system is that he relies too much on spreading the field out horizontally, misdirection and deception. Against disciplined, and athletic defenses this approach gets the Eagles in a lot of trouble.
Another thing to consider is that the Eagles don't really have a good QB. I think Foles, and Sanchez are a result of the system. They're throwing to guys that are wide open, or in the flat most of the time. Kelly is brilliant with his pick plays, and is the best in the NFL at executing misdirections. That kind of scheme will inflate a QB's numbers, I think even a QB such as T-Jack could look decent in that offense. I'd be interested to see what his offense would look like if he had a good QB.
Really, I think Bevell was trying to emulate Kelly during the first 3/4s of the season. In that kind of offense Wilson would be an absolute stud.