All four were okay, but I liked SMRPG the most. It was really fun, and the story was great. To me, Paper Mario seemed like it was totally posing off of SMRPG, only watered down. But it was still okay. Mario and Luigi was funny, but too hard. I really hate the real-time attacking and defending. Paper Mario 2 was good. It was also quite funny and fun. I just wish it wouldn't have had to get "darker" towards the end. As far as gameplay is concerned, here's how I see it:
SMRPG > PM2 > PM > M&L
And graphics:
PM2 > SMRPG > PM > M&L
I always liked the "fake-3D" graphics of SMRPG. You have to keep in mind that real 3D was next to impossible on the SNES. So they worked with what they had, and it came out looking quite nice.
As for music, I pretty much like all Mario music equally, with the exception of a couple really short repetitious songs in M&L.
The stories of all four games were good, with the exception of PM2's ending, which I mentioned earlier.
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