Although, Bay has been quoted as saying he's not interested in doing any more Transformers films. So maybe the next won't be so bad.

Transformers: Revenge of the Fallen — the most terrible revenge since Montezuma's — is louder, longer and lamer than the 2007 hit it succeeds. Which is saying a lot. … [this film] is a grotesque exercise in hyperinflation. At 149 minutes, it's longer than 2001, Close Encounters of the Third Kind or Star Wars. In fact, this may be the emptiest epic ever made.

And, encapsulating what I didn't like about the first film was the continued effort at being a comedy:

Here's a sample of what Bay throws at the wall in the hope of generating some stray laughs: small dogs humping. Hysterical middle-aged women. Autobots with effeminate voices. A miniature Decepticon dry-humping Fox's leg. John Turturro improvising. Tasers. A cowardly Latino. A short Arab. Snails. None of these things is funny. Not in this movie, anyway.

The film currently has a 21% rating on Rotten Tomatoes, compared to the original's 57%.