I played it at best buy yesterday..... played stage 1-1..... you get to be cat Mario in first 30 sec of the game.
It's pretty cool going up the wall, in the previews it look so easy and that there no challenge when your cat Mario but when your playing the game, you need to time when you crawling up the wall because he can only do it for so long before you fall down. IT's also easy to lose the power up, I got a mega mushroom as Cat Mario and once you return to normal size, I lost my Cat Mario power too.
The level seemed very small .... like less then 2 min. But half way in the level I got one of the green star without realizing that I missed the first star. Also there apparently a stamp in every level. So my first intuition after finishing the level was to play it again.
It seem like this game can be marathon in no time. But, from my first impression I want to just replay that first level until I completed every objective.