People seem to complain that games (and movies) are all the same—that there isn't enough innovation. I suspect though that people don't really want innovation. Guitar Hero is innovative. Wii is innovative (watch the Wii video from E3). But if you enjoyed some game, don't you want more like it? Or would you rather take your chances with something random?
In the field of machine learning, there is the notion of exploration vs. exploitation. As you learn things, you want to take advantage of what you've learned. If you never exploit what you've learned, why bother learning it? Why bother learning to read if you're never going to read? However you can't only spend your time doing what you know. You also want to spend some of your time exploring new things. Otherwise you may not discover something better than what you know. 100% exploitation is a mediocre strategy. 100% exploration is a bad strategy. You really want some of each.
In game development, movies, books, etc., it would be a shame if there were no sequels or games similar to existing games. That would mean that if someone discovers something good, we never do that again. On the other hand we don't want only sequels. I think games like Guitar Hero, Gish, The Sims, Everquest, and Puzzle Pirates demonstrate that there is innovation out there. Some people are arguing that there isn't enough. Others are arguing that there shouldn't ever be sequels. It's hard to know what the “right” amount is. I do believe that the way the free market works, there will be slightly less innovation than is optimal. It's not zero though. And I don't believe that you can force the market to innovate more. Ironically, a market with lots of small independent game companies is likely to produce less innovative games than a market with behemoths like EA. But that's a story for another day.
I find that of the games I've gotten recently (Black and White 2, The Movies, Guild Wars, Oblivion), I've enjoyed the innovative games less. I think that's because the sequels have more refinement in them, and that makes them better than the innovative games, which haven't been tried out on a large scale and don't yet have the feedback needed for improvement. I'm trying to spend around 10-20% of my time playing innovative games, in part because I like to study them as a game programmer, but also because I want to spend some of my time exploring new things.
Innovation isn't dead. It just produces lots of junk, which is what it should do. If all innovative games are good, people aren't experimenting enough. Sequels aren't bad. If we never had sequels, we'd never be able to polish the rough gems found in the innovative games.