After Paper Mario: The Thousand Year Door the series turned to stuff, in my opinion.
The Thousand Year Door was the best and always will be the best in the series, hands down. I loving loved that game...it was half my childhood.
I actually agree on this. The first Paper Mario is my nostalgic center but for more solid game play, The Thousand Year Door takes the cake.
Paper Mario was based off of Super Mario RPG, but because that one was made by Square Enix, Nintendo wanted to remake the idea because it sold well. My idea on the reason they themed the game as "Paper" was graphical limitations. If they made Paper Mario a 3D game, it would look like Super Mario 64 wich would make it an entirely different game. The Original Paper Mario did not explore the paper aspect too much where The Thousand Year Door does. Only thing is, I wish I could explore the old world and not be stuck in Rogueport the whole time.
I actually did not like The Thousand Year Door at first because I thought it strayed too far from the original, that and because they changed the jump timing which really messed me up.. However, after those ideas died down I saw that it was a superior game in nearly every way.
I love both those games undendingly.