Super Mario RPG was a fun game that was kept entertaining by the pantomime that Mario would have, dressing up as characters and impersonating them with grunts and other sound effects as he was a silent hero. However, I find the characters in Paper Mario: The Thousand Year Door to be dull and the gameplay lacks the grace that made other Mario RPG's fun to play. In short, Mario RPG's let you do some platforming in a 3d version of Mario's 2d platforming world and let you do battles in a turn-based style with timed attacks. Paper Mario: The Thousand Year Door has a 2d graphical art style, to make it feel like paper. I feel sometimes that areas can be hard to see or known if they are accessible at times due to its graphical setup; you can't rotate the camera and some areas you need to move on blend too well into the background. At least Mario can use abilities like transform into a paper airplane and become literally 2d in order to fit into cramped areas.
The battle system lets you use timed attacks and defend against enemies, but I feel the timing is too strict for some attacks; enemies attack too fast for you to even time properly. I'm not sure if they are unavoidable. I preferred the Nintendo DS rpg, Mario & Luigi: Partners in Time, in which you had to dodge a barrage of special attacks but at least it was avoidable. Fortunately, in Paper Mario: The Thousand-Year Door, the battles aren't too hard, even if you can't dodge some of these moves.
Lastly, I do not like the badge system and 10 item limit, including duplicates. One of the badges lets you do more powerful moves, but they're the same thing in terms of animation. In other words, you can use a more powerful hammer attack that costs flower points (think MP in other rpg's) but get the same animation. When you level up, it is possible to waste the opportunity to raise hp or flower points to boost badge points in order to wear more badges. Then you had to find the badges to equip and some were a waste, like the one that lets you learn Multibounce. Multibounce lets you do 1 damage to all enemies if you don't mess up on the timing whereas your normal attack can do 2 damage to 1 enemy.
I felt the timing for the hammer attack could have been faster too; it's much slower than the jump and the animation does not take timing. You just hold the analog left for a few seconds and release when it's full. Even in other Mario rpg's, such as Partners in Time, the hammer attack was much faster because it doesn't have you wait for Mario to charge it; there is no point in using it on enemies that you can hurt by jumping on them because the jump is much faster, the damage is the same as the normal hammer attack, and the timing isn't as boring.
The game pales in comparison to other Mario RPG's, having you find treasure in the story but it really does not have a captivating story/characters/music that Super Mario RPG had. The battle system is watered down from Partners in Time due to its sluggishness and unintuitive dodging for some attacks.