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Play through Platinum in an emulator to catch up on most of the big changes. Black/White and Black/White 2 are really fun, but mostly because of the story. I think rushing Gen IV would be the safest for your anus. If you only played one of the Gen V games you'd butcher the story.
You could watch a Let's Play of some of the games on YouTube probably. I've never done so for Pokemon, but I'm sure it'd be a quick way to get a taste of the games you missed out on.