SINCE THE widely acclaimed release of Pokeman Red and Blue for the Game Boy in 1998, the basic format of the series has changed very little.
As the main character, a novice trainer, you choose one of three starter types (fire, water, or grass), travel from town to town, more than likely encounter Team Rocket and, ultimately, become the Pokeman master.
Despite the similarities from game to game, Nintendo has never released a direct sequel until Black and White Version 2, which retain all of the improvements from their predecessors but don't do nearly as much to push the series forward.
Right off the bat, Black and White Version 2 are a little disappointing, but since they have even more Pokemon that their predecessors, it won't be very long before you have an entire roster of creatures ready to take on the world with.
The Unova region has changed in the two years since Black/White took place, though you'll still see plenty of familiar faces and locations. All of the trainer gyms have been redesigned, some with new leaders, and there are a handful of towns that didn't appear in the previous game. Additionally, you'll have a chance to capture the black or white version of legendary Pokemon Kyurem, depending on which version of the game you prefer. The events of the previous game are mentioned frequently, and Team Plasma returns for another shot at taking over the Unova region and liberating its Pokemon.
Aesthetically, Black/White 2 are almost exactly the same as their predecessors, right down to many of the same random sprites used repeatedly throughout the game. There are some new trainer and attack animations, as well as minor tweaks to the battle screen, map, and menu, but Black/White 2 treads a lot of familiar ground. This isn't necessarily a bad thing, since all games in the series are similar by nature, but feeling like you've seen it all before only highlights the repetitiveness of the Pokemon games.
As for which version of the game you should pick, there are only minor differences between the two titles. You'll only really notice the difference in the colour scheme, which manifests itself as a black or white version of Kyurem (A dragon - like pokemon).
If you never understood the manic Pokemon obsession, then Pokemon Black and White 2 are unlikely to change your mind, but if you grew up loving the Pokemon trend, then this game is definitely for you.