Seriously, all the Mario RPGs I've played have ended up being awesome.
Super Mario RPG
Paper Mario 2: The Thousand Year Door
Mario and Luigi: Superstar Saga
I'm sad to say, however, that I didn't beat Paper Mario 2 or Mario and Luigi: Superstar Saga, but I did get pretty darned far. In Paper Mario 2, I got to the Final Boss, and it was too tough for me. I think there was some point in the game where I stopped fighting everything that moved, and I came to be a bit under-leveled. Also, the Final Boss's timing was hard to get for me.
Mario and Luigi: Superstar Saga, again, I didn't beat. It's just because I lost contact with the cartridge. I think I was in the last dungeon. (SPOILER)It was around the time when Bowser got a sex change.
Super Mario RPG I beat on an Emulator, so I can't help but think I cheated along the way with Save States. It was one of my absolute favorite games, though. I beat it when I was, like, from 7 to 9. I forget when.
I'm currently playing Paper Mario 1, and so far, it's awesomesauce. But I always take a long time about things. I'm only one Star in, and I think I've found the most that I can, with a time of 6 or so hours.
What do you think of Mario RPG's?