I played it all the way through 1 month ago and it definitely still holds up. The graphics look a LITTLE dated, but other than that...
-Every character is well-written and charming. From the Mushroom Kingdom guard at the very beginning of the game who "left his bazooka at home," all the way to the Nimbus Land bus driver who gives you a lift to the final area, every interaction is a fun one. although I felt that Moleville was a little lacking in development.
NOTABLE EXAMPLE: Booster and his gang of Snifits.
-The soundtrack is PHENOMENAL. Every track fits its intended mood perfectly.
NOTABLE EXAMPLE: Rose Town. When you first enter the town, there's a bit of a... problem. The ominous music lets you know "something's definitely wrong here." After other story events take place, you fix the problem and the next time you enter the town, the music is SO UPBEAT that you really feel accomplished.
-The gameplay is unreal. I couldn't imagine the concept of "Let's put Mario in an RPG ... but it has to be simple enough for beginners" being executed any better than this. The platforming is never frustrating or tedious, the battles are never TOO tough... It strikes such a brilliant middle ground.
NOTABLE EXAMPLE: Sunken Ship. There are several OPTIONAL 3D/Platforming gimmick puzzles that you can play through if you want, leading to 2 of the best boss fights (and one of the best NPCs) in the game
Anyway, yeah... SMRPG holds up very well.