The great, and nearly perfect, thing about Black 2 and White 2 is that these have not been infected with the "third game" syndrome. Instead of having the storyline slightly altered for another legendary Pokemon that once got NO recognition at all from the previous games, these games actually continue from the leave off point from Black and White. It's been two years since the incident at the Pokemon League with N and Reshiram/Zekrom, and Unova has changed a lot.
The gyms have all gotten a brand new layout and each with it's own personalized theme perfectly suiting the Gym's type and Leader. Your rival, a friend from your childhood, is on a quest to find return his sister's Purrloin that she got from her grandfather, after Team Plasma stole it from them years ago. Team Plasma makes a comeback and this time have a much more straightforward goal than last, freeze and conquer the world! You'll be able to travel all over the Unova region in hopes to prevent their evil plan from succeeding, while challenging Gym Leaders, crossing seas and river, and making movies!
So, that's just a little snippit of what's great. I don't wanna give away too much if you didn't want any spoilers, but these really are all great games, and I especially recommend that you continue on with the game you got first, like Black to Black 2, White to White 2.