First there is the particular setting of the case. DC is somewhat different than the rest of the country, since it is not part of a state and therefore there are fewer constitutional issues related to the legislation and licensing of handguns there as compared to most of the rest of the country.
This is contributing to the start of a second round of legal battles against local gun restrictions, most notably in Chicago. Again, both sides have a lot at stake and a lot of money to throw at their lawyers, which means that this case will probably take several more years to wind its way through the court system.
Third, there is the fact that even with a bare majority, Scalia had to do a pretty complicated dance to get this thing together. Namely, there were existing laws against possession of certain kinds of guns (namely machine guns), and against certain kinds of people having any guns, that were treated as sacrosanct. The problem with that (for him, anyway) is that it makes the opinion highly susceptible to a change in judicial opinion. And with a nicely split court that change could not be that far away.
Fourth, Scalia brushed aside various parts of former Court decisions, without actually being able to change them substantively. Those will probably continue to be very important in how judges decide cases, especially given the split in the court for this case.
Fifth, it's still illegal to actually shoot someone with a gun, which rather limits the utility of guns for most "law-abiding, responsible citizens".