Norbit was expected to suck. It's an Eddie Murphy movie, afterall. Transformers was the result of taking a great franchise and wrapping it around a lame plot, weak action, poor acting, and trying to save it by ensuring the female lead played absolutely no role in the movie aside from showing off her boobs. That was, actually, the only redeeming quality of that movie.
Don't get me wrong, I'll still be seeing this one too, but honestly, there really is no possible way this movie is going to suffer from the problem of how sequels are usually worse than the originals.