ok, two-fold:
as a reader, yes, there's that desire, when i read something that is SO good and SO hot to want to see more, to recapture that magic, as you say, and i think: wow, if there was a sequel as good as this, or several, omg! i think that's only natural - of course, sometimes it's better to leave your audience wanting then disappoint them - i have read some amazing sequels, that fulfilled, or came close, or even exceeded the promise of the original - that said, i've also read some that really just feel flat and disappointed me beyond belief.
as a writer, here we go again - sometimes, you just capture the magic and you want to do it again - i think there's more pressure, usually self applied, to create the perfect, magical story that you did the first time, and it can be daunting!
the pluses are: you've already established characters and a setting, you know the material, you are confident that you pulled it off at least once
the minuses: the pressure to recreate something amazing, the fact that, the first time, it was fresh and new, the second time it loses that freshness and becomes more of a job - i'll take my Jenny Grimm series as an example - the first chapter just flowed, it was fun, fresh, it got good response, so i sat down to write another one - it was much harder. for one, i needed to check my source to make sure i got the details right, i felt compelled to try to make it better somehow, in a way, it was a little like rewriting something, and therefore not quite as fun to do - i found myself wanting to explore other ideas that had nothing to do with Jenny, or would be out of place in her story...
don't get me wrong - i LIKE doing sequels, giving characters a life of their own, but it's different then writing a one off story - plus, there is the pressure of getting a story out while it's still fresh in the readers mind - putting out a story once a week, keeping them rolling as fast as people would like to read them, isn't easy, and it can kill your creativity or love of the story, and yet, putting them out months apart can kill the momentum as a reader...
just my thoughts.