This will be the first numbered sequel to a traditional Pokemon game; previous generations have consisted of two initial releases followed by a single, similarly-titled "enhanced" version: Pokemon Diamond and Pearl followed by Pokemon Platinum, for instance. Now, however, we'll have Pokemon Black 2 and Pokemon White 2. Whether this distinction is purely cosmetic or carries heavier gameplay implications, remains unclear. All we know for certain is that, by now, the PokeRap must be several hours long.
Update: A statement on the US Pokemon site calls the games "Pokemon Black Version 2" and "Pokemon White Version 2" and says that details will be sent out "throughout the year." Looks like the game is heading to the US as well -- surprise!