I lover Super Mario but I admit I've been feeling it's been getting a little stale. My last love in the series was Super Mario 64. I thought Sunshine and Galaxy were great games but they just didn't do as much for me. I own Galaxy 2 but I haven't played it much at all.
Super Mario 3DS is for some reason perking my interests more than a Mario game in years. It's a 3d adventure (not a sidescroller) where they claim they've found a way to help 3d precision be as precise as 2d (so hitting a ? block will be just as easy in this 3d game as it would in a sidescroller). Whether that is true remains to be seen. It might be just because of the 3D of the 3DS that will make depth easy to read.
Small Mario is returning. I assume once you get hit you turn small. Really it just looks like a return to the classics. Like Super Mario Bros 3 in 3D. Though I can't say for sure since there's only like 4 screenshots...
But seriously, look at this logo and look at what's returning!
http://gonintendo.com/wp-content/photos/supermario3ds_gr.png
I'm really excited for the 3DS. 3D without glasses WILL really help with depth issues in 3D games (where you'll often think that jump isn't that far... but it is ;P). Too bad the launch games suck.

Here's the very limited screenshots we have of the game...
http://gonintendo.com/wp-content/photos/mario_3ds.JPG
Comments
And hurray for the tail, which alludes to the raccoon suit thing! Hurray for the Classics!
People said the Wiimote was gimmicky. It is. But when paired with an awesome game that uses it in an awesome fashion it's awesome.
3D will be the natural progression of graphics. Depth REALLY does help a lot in 3d environments. It'll eventually be like color TV and become the norm. However, a lot of mediums treat 3D terribly. For instance when movies design scenes JUST for the 3D like slow motion TRIBBLE heading towards the screen or a freakin' yoyo being yoyo'd towards you...
When 3D is respected and treated well and intelligently and not thrown in your face for the sake of being 3D is when it's used right.
However, I admit 3D has a long way to go. First off it's still not perfectly natural looking. 3D in real life looks a lot different than 3D in games and movies. Also most mediums still use graphics and we don't have the technology to make it otherwise unless it's a one person electronic like the 3DS. Also it can make your eyes hurt because they try to focus one something only fooling you about it being 3D.
Then... less than 10% of people have 3D problems and can't see it properly anyways (10% is a lie, it's much lower when it's 3d produced more naturally like the 3DS which lowers that statistic significantly).
I predict one day 3D will become standard. I predict it won't be abused like it is too often these days. I predict that it'll become so standard nobody will notice anymore like the Rumble in controllers.