>>58258511BW2 has story continuations but you could more or less piece it together, especially if you talk to NPCs.
However, I would note BW2's campaign skips notable locations that BW features pretty prominently, and while it adds it's own extra areas, BW's Unova is the one I think of when I think of Unova.
Not saying you can't start with BW2, there's plenty of reasons it's better than BW, I just think BW represents Unova a little better.
