No, it's not a gimmick. It's a very well-designed, very well-run, very disciplined system designed to be different, yet easy to run, with a pace that keeps defenses on their back-foot, and utilizes talant that other teams and other systems find no use for in a traditional system, but still have exceptional talent (i.e. guys liek Woodhead and Welker).
That, and it's run by the greatest QB who has ever played the position.
That helps I hear.
So no, it's not a gimmick. It's just good.