Perhaps, given the negative reactions to ROTF,
Transformers 3 will see a noticeable drop-off in box office returns. It's happened before:
The Matrix Revolutions grossed much less than
The Matrix Reloaded, and the domestic total for the 3rd
Pirates of the Caribbean movie was noticeably lower than the 2nd film's take (however, it did do better overseas, resulting in the worldwide total not being significantly less than that of its predecessor - well, if you can call around $100 million not too significant, which you arguably can when you're talking about close to a billion dollars

).