I picked up Super Paper Mario today, and Xavier and I spent pretty much all evening playing it.  He's finally old enough to be interested in the words, so I'm basically reading aloud all the text in the game.  Some of the characters are pretty fun to give voice to, I have to admit.  In general it's pretty fun, though far more of a platformer than the previous Paper Mario games.  That's not inherently a bad thing, but I do miss the Mario RPG vibe.

A key gameplay mechanic is switching between the 2D and 3D representations of the game, which is a very clever little gimmick.  I don't know whether it will have enough legs to still be interesting by the end of the game, but it's a great deal of fun so far...