To be honest, Super Paper Mario is so far the most boring Mario game I've played. I play a lot of games with major stories as I'm a RPG fan, but the story is boring and I've got the feeling I'm more talking to characters than I'm playing through the game. More bla bla than action.
Haven't finished it, as I got tired at the end of world 2. And when I read it gets worse after world 3, I'm not so sure if I want to finish it. I haven't played the Cube version yet, as I got it since recently so please tell me this game is more fun and interesting? The N64 version is without a doubt a lot better.
If you think that this game has the deepest story in a game ever, you better play a Star Ocean III, Xenosaga or even a Final Fantasy XII first ;) Now that's what I call a deep story.