Movie history is filled with examples of sequels that sucked. In fact, there have been so many that the ones that were as good as the original are celebrated-- The Godfather II and Aliens come to mind.
Kim sent me a link to a Vanity Fare article in which Paul Giamatti discusses his plans to film a sequel to the 2002 cult classic Bubba Ho-tep.
A couple of other bloggers have mentioned a love of the movie, specifically Vikki and Bubs. For those of you who aren't familiar with Bubba Ho-tep, I'll clue you in. Bruce Campbell portrays an elderly Elvis, who is living in an assisted care facility. It turns out that he switched identities with an Elvis impersonator, er, I mean, an "Elvis tribute artist" and is still alive. He befriends another resident of the home, President John F. Kennedy-- yes, that President John F. Kennedy-- who is played by the late Ossie Davis and has a perfectly good explanation as to why he's now black. I'll let you see the movie and find out.
It turns out that a cowboy-hat wearing mummy is stalking the elderly residents of the nursing home and stealing their souls. It's up to Elvis and President Kennedy to stop the soul-sucking mummy.
In Giamatti's proposed sequel, actually a prequel, Col. Tom Parker, played by Giamatti, signs Elvis up to do one more movie. Somehow, hot female vampires get involved in it all. And it takes place in New Orleans. And I put it to you-- what more can one ask of a movie? You've got Elvis, Paul Giamatti, New Orleans and hot female vampires. Sounds like a winner to me!