The Q.B. was supposed to make a pre-snap, no-matter-what check into another play based on the number of defenders in the box. It's why we frequently got down to 1 second left on the play clock, because defenses could shift around and screw with the Q.B.
We ran some, but other than Long's playback, it was always the basic zone out of the shotgun. Very little variety or command to it.
It had all the drawbacks of a spread without many of the benefits.