I think portals was very innovative, and it sold great. Same with HALO, rayman and same will it be with spore. Big companies make great new innovative games (and if they are sequels to the previous story, it doesn't mean they are not innovative anymore).

If you drag one idea too much around, the public will discard it as well. Especially if your new "same-idea" game turns out to be worse than it's ancestors.