I'd have to disagree. At least about the redundancy of sequels. Nintendo isn't as guilty of cookie-cutter sequels as others. They have a lot of games, yes, but the games are often different enough.
Mario has his spin-offs, but I think Mario's actual adventures are slowing down, if we don't count his RPGs. Three games on the NES, two on the Super NES, one on the N64...and most people (including myself) are hesitant to want to count Sunshine. It was a good game, but it didn't feel like a full Mario game being limited in locale. So it's like half a game. (Next, we may only get a quarter of a game...) Not all changes are popular, but the inclusion of FLUDD was an attempt to create a different sort of Mario platformer. I'll admit that Mario Party is getting redundant, but that's probably why they included a microphone in the last two iterations and 8-player in the latest one.
Metroid entered 3D, and then included a light/dark world dynamic. Sure, it's been seen in other games like The Legend Of Zelda: A Link To The Past and the Silent Hill series and others, but it also had completely new Suits. Yes, the multi-player was lackluster, I'll admit that.
Link has had the most 3D games, four compared to Mario and Samus's two each. So by the time Wind Waker was to come around there was already Ocarina Of Time and the unique-3-days-system from Majora's Mask. The most obvious difference in Wind Waker was its cel-shaded look, but the game also had sailing. I personally didn't like the sailing, it took too long most of the time, but it was an additional gameplay element nonetheless. And Twilight Princess has the werewolf thing going on. One thing about Zelda games is curious; everyone (who isn't a major fan) thinks it's always about Link saving Zelda from Ganon, but until Wind Waker, every game introduced a new villain (that is, if you count Ganon/Agahnim/Ganondorf as separate) and the games come in pairs, it seems, with one game in each pair not involving Ganon (or one of his other forms) as the final boss. So it only happens half the time, which is as close to never as always, technically. I think it's the Ganon ones that sell better, but that's (kind of) beside the point.
I think my original point was that Nintendo hasn't hit a brick wall when it comes to coming up with something actually new in sequels. I think the thing is that consumers care less about the characters and situations regardless. Especially those that are more plot-based than gameplay-based. I probably went off on a tangent there, but I would agree with Ian's last point in the particular regard that the controller will add "newness" to continuing franchises, and this difference is more immediately evident than Samus finding herself in two intertwined worlds, for example.
I just hope I'm not playing the exact same games by flicking my wrist up instead of pressing A to jump, but as I pointed out, Nintendo should still be capable of coming up with new things in sequels.