The secret to not being disappointed by sequels you are excited for:

Expect it to be 10-20% worse than the previous instalment in the series.

This way a) you are prepared for said movie to not be as good as the movie(s) that came before it and b) if it totally kicks ass, it's an extremely pleasant surprise.

It should be noted that this will not always save you (Spider-man 3, yes, I am looking at you.)