Paper Mario: The Thousand Year Door is essentially the first Paper Mario with a new paint job.
Wut? I mean, okay, some partners and superficial narrative threads were similar, but otherwise it was plenty different. I don't see the game's mechanics being otherwise largely identical as surprising and/or bad, if that's what you were getting at. The only criticism I'd give TTYD is that the areas were more linear than in the original PM and the fetch quest before heading to the moon was aggressively annoying.
Also, for the record, I'll still stick up for SPM.
Partners in Time, though, now
that game was shamelessly repetitive.
Mario is your oyster.
Best N64-era print ad tagline that never was.