>>50186245Platinum has the most intellectually titillating plot and the highest stakes. It's the first game to take you to an alien realm. The musical score is largely praiseworthy. The addition of cross-gen evolutions makes you excited to pick old mons to add to your team.
Platinum's reputation largely rests on the postgame battle facilities and functions, as well as the expansion of the dex and mechanics from Gen III. It's a middle ground between the relative primitiveness of RSE and the nu-sensibilities of BW.