We already voted Super Paper Mario for the Nintendo Wii into the top 5 must have product releases for April. IGN published a review of the new Mario game already with video.

Quote from the review:
"You should buy this game for a number of reasons. It's a Mario game and for some that will be enough. It's also one part platformer and another part RPG, successfully dabbling in both genres. It controls tightly and uses the Wii remote in a smart manner without stepping into forced territory.
The new 2D-to-3D dynamic is built around clever and surprisingly complex puzzles that will challenge and impress you. And it all comes together to make Super Paper Mario a highly enjoyable title, whether you want to call it a platformer, an RPG, or something in-between. You will have fun and the fun will last for a good while, plain and simple. "
Read the full Super Paper Mario review on IGN.
Amazon.com takes pre-orders for Super Paper Mario and updated the shipping date to 13th of April (from 10th of April). The price is $44.82