It's a great game!
It's a platformer, but a difficult one, so it might take a bit to beat some of the tougher levels (Polar Knight is pain, just a heads up; also the Tower of Fate levels made me very happy there wasn't a lives system, prepare to die a lot there), but you have infinite lives so you'll get through 'em eventually. I dunno if it has a nostalgic feel (I only played the Marios, the GB Kirby's Dream Lands and Zelda II back then), but it has a very fun feel, and I like that.
I dunno about the hype, but if you've heard it's great, then you've heard correctly.
Also there's another campaign with a different story and character with a very different playstyle coming out soon, which has me excited!
I got the 3DS version, which is portable, has some 3D stuff (apparently; I never really noticed) and has a Streetpass thing I never used.
The WiiU version has a multiplayer mode and probably other things, but I didn't get that one so I dunno.
Also they're releasing a physical version in October for both of those (at least I think it's both of those). Not sure that impacts your decision, but I might as well mention it.
Overall though, it's a great game and you should play it!
One piece of advice though: You can break checkpoints by attacking them. Doing this gives you money, but makes the checkpoint stop being a checkpoint. Good for the extra challenge, but not something I'd recommend for a first playthrough. Just letting you know.