Which of the Gen 5 Pokemon games to play?

Honestly, it's worth playing both. Generation 5 sets a new trend by focusing much more heavily on plot elements and more than just 'become the champion' which is a nice touch. Black/White are the first part of the series, and have solid gameplay, a heavy focus on Gen 5 Pokemon, and a large number of fun tidbits scattered throughout.

BW2 on the otherhand is a direct Sequel to BW and takes up the story of BW two years later in Unova, furthering this new direction on a focus of storytelling elements.

Gameplay wise Gen 5 is much improved over gen 4 in many ways, and Like Black/White BW2 also includes a salvo of side events and missions that will keep you busy long after you mange to finish the main game. The best way I can describe it is...

If you've ever Played Pokemon Mystery Dungeon 2 Explorers of Sky you'll notice the similarity of a sheer number of extra things to do long after the main story is done. 300 hours in BW2 I still have things I can do. (Game Devs take note!)

Really, BW/BW2 offer huge replayability, intertwined stories that connect well (and are enhanced by playing them in order).

BW and BW2 have more differences than just Pokemon. Cities for example change in their respective versions. Opelucid City and Black City/White Forest are prime examples of that.

I ended up getting all four new when they first came out, but I know not everyone can, but I'd encourage at least picking up at least one of BW and BW2.

Oh yes, BW2 also offers a key system which further enhances gameplay. Not to mention Pokestar studios or any of the other features.

Really, the versions drop down to personal taste though. Yes, they are different but it ultimately depends on if you feel that they're different enough to justify purchasing both Black and White or Black and white 2.

B2W2 are like improved versions of Black and White, there are a lot of new features like White Tree Hollow, you get Zorua, Latios, Heatran without event/cheats, etc. Most importantly, in Black and White, you could only see prev Generation pokemon after beating the elite four. In B2W2, you can catch awesome pokemon like Riolu, Growlithe etc near the beginning of the game, before the 2nd Gym. So in my opinion, B2W2 are the better games.

Out of Black2 and White2, I would choose White2 mainly because you get Rufflet in W2 and not B2. Check this page to see all the Version Exclusive Pokemon:

http://bulbapedia.bulbagarden.net/wiki/Version_Exc...

I have diamond,soul silver and white 2.If you really want it then get it but in my opinion some of the new pokemon designs are copies of some of the older ones,all of the games have the same basic premise but they're all different in some ways.At first I didn't like white 2 but its ok after you get used to it.The newer legendaries aren't as cool because none of them roam and the main legendary is ok not awesome as mewtwo or dialga imo.