Not OP, but I think it's not too crazy to think Paper Mario is one of the best RPGs of 5th gen. I wouldn't call it the absolute best, but it's up there along with Panzer Dragoon Saga or Suikoden II for me.
Calling it a "my first RPG" isn't really a solid argument since Final Fantasy VII was probably the actual first RPG for most people, I understand you probably say that because of Paper Mario's simplicity and not because of actually being the first RPG people play, but I think even within its simplicity it excels at what it does, when it came out (2001) I was kind of burned out of RPGs, and Paper Mario with its simple but effective badge system felt like a breath of fresh air.
I mean, it's not like Panzer Dragoon Saga is overly long or complicated either, it could also fit as a "my first RPG" experience, only difference is that instead of being set on Mario universe it's on PD's universe so it may came off as less "kiddy"... but honestly? I played PM as a young adult and I fucking loved the writing, humor and characters. The plot wasn't anything special but the whole game felt alive and characters were well written, never thought I'd care about a Goomba or a Koopa Troopa on any game. Intelligent Systems (and I guess the localization team in the west) did a good job at giving generic characters from the Mario universe a lot of personality and charm.