He just lost to freaking Robin Haase (a fellow countryman of mine as well). That is a rather embarrassing mark on his career in my opinion.
In any case, if the AO2014 remains his only slam (and I think it will), I don't think he'll be remembered any more than a lot of one-time only slam winners. Less than Del Potro I think. Winning a masters title isn't going to change much, and outside of that one AO2014, he is solid but not very spectacular in his results, still generally losing to the top players even if he makes it close. So I don't think there will be much of a legacy. Nevertheless, his career is very successful and he's a very powerful tennis player with a huge backhand, that's what I'll remember him for.
Also, I fear that people will remember that AO more as the one that got away from Nadal to win title no. 2 there, especially if he never wins another one, and that's looking quite likely now.