Bit Tech just published an editorial that talks about why sequels are a good thing:
It all comes down to that age old nightmare – game design. As I've said before, design is hard – it’s certainly the hardest thing about making good games. As an indie developer, I get to do all the jobs, and the design bit is the one I find hardest of all, although ironically it's the bit I get praised for in reviews. I'd like to put forward the theory that the difficulty of design is a reason we should love sequels. Let me explain...
I worked for three years on Lionhead’s The Movies and I ended up being known as the AI coder even though I actually worked on lots of different parts of the game. Because I was involved more or less from the start of the project I saw the game design evolve over time, which it did rather dramatically.
If you haven't seen The Movies, let me describe it briefly. The Movies is a management game where you run a movie studio, with a 3D view of your studio lot. You pick the actors, sets, costumes, and (and this was the cool bit), you actually got to see the finished movie that you made, with the option to add subtitles, sound effects and so on.