Hard to tell in some of these images where the focal point would be. Also looks like you used a large aperture for shallow depth of field, that makes judging focus a little more difficult with this set.
I just did a shoot with a D800 + 50 f1.8G this afternoon (ok, it was just my kids!) but I was very happy with that combo. Used it mostly at f1.8-5.6 and sharpness was not an issue.