As far as the happy ending goes overall, JKR wasn't going to make it a sad ending. I think some fans anticipated that, or at least something bittersweet, and... that's not the sort of story JK Rowling was going to tell.

Imma be honest, a lot of people who complained that it was sappy and saccharine would have been perfectly happy with a sappy, saccharine ending that featured their pet pairings and/or headcanons.