Pigs can't fly, but fat plumbers - apparantly - can.
The sheer amount of freedom felt, to go anywhere - at the pace you chose - feeling like you could jump over anything?
This game gives that feeling back, shortly after the introduction.
As soon as you land in the first actual level, run completely around a planet, up a wall and jump to another planet - it just feels like freedom (despite the fact of you being stuck in a room behind a TV screen).
It is just a game where, if you think it can be done - you can do it.
Mario's actions aren't much more varied than previous titles (only one new move, really - replacing another one.) But the environments work so well with the actions you can perform, it doesn't really matter.
The cast is memorable, although you probably already know most of them. The levels are memorable as well, colorful and rich with things to fool around with, large as well.
For the same reasons, it isn't noticeable that mario's transformations are a lot more limited than previous titles of the series.
There are some platform challenges. But since the game is just a blast to control and play - you will blast through it in no time.
It doesn't take itself too seriously, but offers some serious gameplay and replay value - replaying the game is something I do just for the hell of it.
In other words, it's an experience - and a certain green heroe is playable at the end of that experience, and controls differently enough to warrant the second playthrough.
A must-have!