My favourite Paper Mario yet.
However, there are a few problems. While in 2D, the game looks great, with a fantastic artstyle. However, as you switch into 3D, the game gets downright ugly. The environments are bare at best, and don't even compare to the 2D environments. Also, the game is definitely too easy. Some of the pixls make the game very easy in combat (although you can always opt not to use them) and most of the platforming elements are far too easy. However, if you are really looking for a challenge, the optional Pit of 100 Trails will really offer some difficulty.
In conclusion, Super Paper Mario is a great game that will keep you busy for a while.