They made this game its own thing and not paper mario or made this game before it's proceeders. The former because if it was it wasn't a paper mario game, we wouldn't expect it to be like the first three like we all loved. The latter for a similar reason, and because we would see a great rise in quality throughout Paper mario history. It would make more sense, because we went from a classic story to a unique story, to an even more unique and outstanding story, to, well, not a classic story, but still a Bowser kidnaps peach story.
Other than what it wasn't, there's not much about this game that stands out, and I'd probably just forget it existed if it weren't a PM. --- "it's that game that is so great it makes you want to destroy your Toilet." -Throwback2780 See how my mustache moves in the wind!