Sequels.

I was hugely disappointed in "Clerks II." I finally saw it last night, and it was not nearly as funny or as quirky or as smart as the original. Dante and Randall are so old now, and Kevin Smith has to stop putting his wife in his movies.

Maybe if Smith didn't wait a decade before making the sequel, it might have been better. And it is quite possible to make a really good sequel. Here are a few that I think are just as good, or even better, than the original:

Back To The Future II
Superman II
The Empire Strikes Back
Indiana Jones and the Temple of Doom
Terminator 2
The Godfather, Part II
Rocky II (although Rocky IV is the best in the series)
Aliens
National Lampoon's European/Christmas/Vegas Vacation

I'm sure there are others, but this is all I can think of at the moment.