THe 'treat' we were shown at the Paramount party was a couple scenes from the movie, and one was the merging of Devastator. And the impression many of us got was that the central figure appeared to be absorbing rather violently the smaller figures, almost against their will. It was a fairly lengthy scene, like the intro of Optimus in the first movie.

THe other scene shown, for those wondering, was Bumblebee fighting 2 Decepticons. (not saying here who, because it's a spoiler).