I think just the idea is somewhat different from games which are out there. After that, we'll see how successful we are. The trick is to have elements which player's will be familiar and comfortable with, sprinkled with new and different ideas or paradigms. I also think this industry has been focused on sequels. There's a good reason for it.
People are comfortable and familiar with a sequel.
If they liked the first game, you can almost guarantee they'll buy the sequel. That makes it a no-brainer decision for developers and publishers alike. I don't think it's necessarily a bad thing. There have been some great games which were sequels - Jedi Knight, Warcraft 2, etc. From my standpoint, I don't care if a game is a sequel or not, as long as it's a great game.