Let's forget, for a moment, whether or not you like the sound of the title: Transformers 2: Revenge of the Fallen.
Instead, let's focus on the meaning behind the name of the Transformers sequel.
According to CHUD, "the Fallen" refers to one of the original 13 Transformers created by Primus.
The Transformers wiki provides background to this theory:
At the dawn of time, Primus created new life, the 13 original Transformers, to crew his planetary form into battle against his eternal nemesis Unicron. One of these 13, his original name now lost to the mists of time, turned against his siblings, his creator, and his universe, and betrayed them all.
...this guardian of entropy became obsessed with the darker side of chaos and death, and in the black place these urges led him, the betrayer found a new god, more suited to his nature. He turned against Primus and became the Fallen.