I loved Paper Mario 2. I own Mario RPG and the two Mario & Luigi's, but yes, I never played the original Paper Mario. And I feel sad about it. Which is why I really hope Nintendo makes it available to download on the Revolution.
The only thing I hated about PM2 was the leveling up system. No Experience, just flowers that if you went back to earlier enemies to level up, they gave you less points than they used to. It just seemed too frustrating to level up in PM2.