When I first played Super Paper Mario I found it to be very boring and easy. After playing through the first chapter I gave up on it and it ended up sitting on my shelf for a couple months. After that, I decided to give it another shot and picked up where I left off, and to my surprise I really enjoyed it (although I can't see myself playing through it more than once).
And if you're enjoying paper mario so far I'd suggest getting PM:TTYD. It took what PM did and greatly improved on the graphics, battle system, and story.
In my opinion: TTYD > SPM > PM (even though it's still one of my favorite N64 games)
And even though SPM is my favorite game for the wii (that isn't a port), I'd still prefer the next PM game (if/when they make another) to be an RPG.
