I beat Mario and Luigi a few weeks ago, and I must say, it was a very enjoyable little romp. I don't know if it's really fair to compare Mario and Luigi, Paper Mario, and the original Mario RPG because they're all so different games, so I won't dive into that. It was interesting though how the game was so easy, and then, WHAM! You get to the final boss. It took me four or five tries to actually beat that villian.
But in the next Mario RPG game, they really, really need to have a rideable Yoshi in the game. That would make me such a jolly bird, it would.