Gonna go against a few common arguments here.
"They're all the same. Just look at the two Galaxy games."
Typically, the strongest element of a platformer is its level design. Because of this, you don't always need a huge list of new features in a sequel. Normally, they do a lot to mix it up (compare Mario World, Mario 64, Sunshine, and Galaxy 1), but the feeling I get is that they didn't get to do everything they wanted with Galaxy 1. Galaxy 2 has fantastic level design, so I don't mind that it took the original mechanics and added a few new power ups.
This also tends to pop up against Zelda. I like to point out that not only are the level design of the dungeons and boss-fight mechannics important enough to carry the series, they also tend to put twists into an endlessly repeating legend to add some freshness to the plot. Not to mention the series tends to occasionally use a completely different art style.
The third biggest target of this criticism seems to be Pokemon. Honestly, I'm more of a casual pokemon fan, so someone else maybe able to go into detail on that one. I know the math behind the combat gets more complex and the number of pokemon to choose from continues to grow, and that's pleanty of variety right there.
"They're lazy...the new Donkey Kong and Kirby are sidescrollers."
I don't get why making a game in a certain style is a sign of laziness. Sidescrollers are not inferior to 3D; they are simply different. I think it's great that Nintendo is getting in on the retro movement that's been popular with platformers and fighters, and I'd love to see it catch on in other genres (especially RPGs and Shooters)
"They keep using the same franchises. Where' the originality?"
Actually, they've been releasing at least one new franchise per generation. In fact, the only nintendo platform I can't recall having any new franchises is the gameboy color.
Arcade--Mario
NES--Legend of Zelda
SNES--Star Fox
N64--Super Smash Bros.
GCN--Pikmin
Wii--Wii [Noun]
GB--Pokemon
GBA--Golden Sun
DS--Nintendogs
It's not that they don't come up with new franchises...they just keep most of them alive throughout the years.