I'd like to be as excited for the Backgrounds as most people seem to be, but for me there are two big concerns with them.
1) They might be the new default "space filler" for future WotC books.
This is a recent concern - in the playtests, backgrounds were several per page. No way they could be a space-filler effectively.
But Basic has shown that they can easily fill an entire page with the new format that extends to include the RP-boxing-filling elements, and my concern is that with the PHB, we're going to see them at 1/page (in fact, I will be shocked if not), and that in any future book which contains player-oriented info or setting material, we're doing to see a dozen plus backgrounds, essentially just taking up space, because they can only be used with new PCs, and only ever have any effect once.
So they could be a particularly useless space-filler.
To be clear again, conceptually, I like them, but I am pretty worried about this. I think it's very likely.
2) The alignment suggestions vary from the "Okay" to "OMG WHAT?!". I wish they'd just left them out. It's easy enough to say "ignore those, they're nonsense!", but I think that they're actively counter-productive and will put bad ideas into the heads of players. For example, the idea that mindlessly following orders is "Lawful" and thinking for yourself "Chaotic" seems like a simplification of the absolutely worst kind (it's not entirely wrong, it's just kind of "Oh jeez...").
So I picked the middle option. Like the concept, fear the implementation.