From the questioning during orals something like this was expected to be the decision. It was also almost certainly going to be a 5-4 decision. Nearly all the cases released this late in term are. The longer the debate the later the decision.
Just finished reading the decision about a half hour ago. It went farther in a couple of areas than most expected. Since the 2nd Amendment has never really been touched by the court since ratification back in '91 it was interesting to see how much they relied on contemporary reasoning and how much historiography was used.
Aside from the ruling itself the biggest thing to come of it, however, is that even though it's a 5-4 split it's a decision that should hold up over time. It's also not so specifically written to just the Washington DC statute that brought the case initially that the ruling will be applicable nationally.