Having played the first two Paper Mario games repeatedly (read: at least 6 times each), to say that I was eagerly awaiting SPM, is an understatement. Before dissecting the game proper, let me say that I was not disappointed. Yes, SPM stands apart from the two previous titles from it's gameplay, the spirit, great humor and wonderful artistic style are still bursting from the seams.
I have to say that I love the 2D to 3D mechanic. By itself, a platformer in this style would have been very shallow, and boring, but being able to have a secondary world with the flip of a button created a world (pun intended) of possibilities. I've spent a lot of time going back through each world in 3D, not only to find the secrets, but just to see the details from the 3D perspective.

The gameplay is very easy to pick up, and the in game text offers generous hints. That said, one of the issues I do have with the game is that it is too easy, especially for an experienced gamer. However, the purpose of this type of game isn't just the challenge, it's the experience, and Intelligent Systems have put a lot of effort into making it a complete experience.
Just like the previous titles, there is too much back tracking, and I would have argued for 6 levels in each world, rather than 4, but those are minor gripes.
Even after beating the main game, I'm not going back through and completing the side quests, with about 35 hours of gameplay time so far. SPM is a great a welcome addition to the Wii library, and I certainly hope for a sequel, either in this form or in the more traditional RPG style.