Edwin - I disagree that Nintendo aims at the pre-teen set. Their games aren't going for the teen-to-manchild demographic of stuff like Call of Duty and Halo, but they have a broad appeal with gamers and non-gamers of any age. Just because something isn't violent and full of cursing doesn't mean it's meant for kids any more than something full of profanity and nudity is necessarily "mature." Personally, I'd rather play a creative Mario game over anything gritty and aimed at adults.
Nintendo banks heavily on Mario, but they are some of the best games ever made. Literally. GameRankings.com's top 10 games of all time by rating are, in order: Super Mario Galaxy, Zelda: Ocarina of Time, Super Mario Galaxy 2, GTA4, SoulCalibur, Super Mario 64, Uncharted 2, The Orange Box, Metroid Prime, and Tekken 3. That's 3 Mario games, 1 Zelda game, and 1 Metroid game. No first-party Microsoft games and only 2 PlayStation brand-exclusive games. (I should note that GTA4 is ranked 4th for PS3 version and 6th for 360 version and the Orange Box is the 360 version). So my point is that Nintendo makes high quality games and continually does so.
That said, it's extremely disappointing that the best game of the last generation (from one standpoint) was Super Mario Galaxy and their new console launched with a game that looked/played more like one of their best-selling games, New Super Mario Bros. Wii. I want to see their brand-new take on a classic franchise. The Mario 64/Galaxy, the Zelda: Ocarina of Time, the Metroid Prime. Pikmin 3 is good and all but its basically the perfect version of Pikmin 1 and 2 instead of the NEW version. Their are big rumors about the new Zelda and I'm sure they're working on tons of great stuff that nobody has seen, but it's a bit disappointing.
There's no reason 3rd parties aren't also doing amazing things, but hopefully Wonderful 101 can be an example of that. Unfortunately, I don't think that game will have mass appeal.