Nintendo and Mario at their best.
The game combines aspects of both RPGs and platformers, as you probably already know. Although this doesn't seem like it would work too well, it flows perfectly. Based on your amount of points, you level up and gain health, strength, etc. This is a great way to get gamers to actually fight enemies because many players just skip past the baddies in other Mario games. It offers an incentive to staying and fighting, which is something not usually associated with a platformer.
The gameplay is amazing. The different abilities that pixls grant Mario keep you guessing as to what is going to happen next.
The graphics, in Paper Mario fashion, are cute, bright, colorful, and work very well.
Sound is somewhat disappointing as the background music is an extremely simple loop tape, and the traditional Mario jumping sounds, etc. are all still there.
Overall, Super Paper Mario is worth the MSRP $50, and I would recommend that any Mario fan should pick up a copy.