Mario games are the s***. Mr BenKenobi88 said it well.
I look at it as a qaulity assured stamp on the game, wether it be mario, golf, karts, tennis, rpg, whatever. If its a mario game you know its gonna meet a high level of qaulity and have that classic style and humour.
Me I cant get enough of Mario.

^^ Sonic Rush is an EXCELLENT game - and it's set where Sonic should be - in 2D.

And Hus... NSMB didn't sell FOUR MILLION in Japan ALONE because it has Mario on it - because it is one of the best games of all time. Period. And it's still selling. And guess what? We haven't had a game like NSMB since 1994. Yeah.. that's soooo milking. Like the 3D platformers. Unlike Crash [4 on one console?!] R&C, J&D etc we get ONE excellent game every generation which totally blows the rest out of the water.

No way mario is awesome! Ben i can't believe you forgot Mario golf...that was def underated.

What I would suggest to Nintendo is to open up the Mario games to other franchises, as they have SSB (note the lack of the name Mario in the title - he's just one of many supporting players). While I think the Mario Kart name is too well established, why not Smash Tennis, Smash Golf, etc, so that other Nintendo (and maybe 3rd party) franchises could get in the mix as well. Honestly, as good as those games are, it'd be nice to see more variety in level design and character selection.

 I've just checked a review, it scored very well. Unfortunately, I don't have a DS. I'll see if I can persuade my little brother to get it.

Pokemon, Brain Training, Animal Crossing, Kirby, Kid Icarus, F-Zero, Excitebike, Zelda, Metroid, Starfox, Donkey Kong, Yoshi, Pikmin, Pilotwings, Wii Sports.

What is the problem? What company has created more successful video game franchises than Nintendo?

I really think Zelda is a much bigger franchise than Metroid. Don't forget, as far as BIG franchises, they also have Donkey Kong and Star Fox. Some lesser credited franchises: Kirby and F-Zero. Some of their newer franchises: Pikmin and Animal Crossing.

On Topic: If the Mario spin-offs were complete crap, I would complain. As it stands, they are not. 

 Wait.  Where do Wii Sports and Wii Play have Mario?  You could *sort of* make a Mii that *kind of*
looks like Mario if you look at it sideways through a bong, but I'm certain that Sports doesn't have 
him built-in, and if Play does, it's have to be some sort of brief cameo, as I do not recall him at all.  

Anyway, to address your point, Nintendo has a few other franchises than what you listed that are 
Marioless.  I've no idea why you forgot about Zelda.  The Donkey Kong series is popular, and 
although it birthed Mario, its games don't feature him.  Kirby is Nintendo-published, so I don't 
know if that counts.  Nintendogs is a *gigantic* franchise, especially considering its age.  Ditto for 
any of the "training" games, especially the two Brain Training, which have shown that the genre's 
incredible success can last into sequels.  Pilotwings is a million seller.  Animal Crossing is a multiple 
million seller.  Starfox is big enough that even a crappy entry in its series can sell over a million
(not all of them, though).  Pikmin was a million seller on Nintendo's weakest ever selling console,
so it has some potential for hugeness.  The WarioWare game might be pushing it, since Wario is 
basically a Mario derivative, but I don't know if Mario himself is in it and it's sold multiple millions.  
Anyway, Nintendo still apparently has rights to the Tetris empire on at least portable consoles
(since they published Tetris DS).

Nintendo also recently purchased Monolith Soft recently.  They developed Xenosaga, which I know
nothing about, but Wikipedia claims (sans citation) that it "was considered a best seller in Japan
and US".  They also make the Baten Kaitos games, which I've seen a little of (my girlfriend really
likes rpgs, though she's only been able to latch me onto Symphonia), but I don't know how big it
is.

So Nintendo does has more than two non-Mario franchises, even if you ignore the ones whose
characters are linked to Mario (like Wario and DK). 

[edit: Vgchartz's rich text editor hates my web browser.  Any way I can set it to use a regular
plain text editbox?]

You really should. It is awsome. And the new Sonic Rush adventure is coming out which looks to be even better. Sonic is fast, cool and much better than his 3D ones. Even the 3D boss battles are AWSOME.