Supposedly the G3 is a tiny bit more sleek and trimmed down, but I cant see it in images (barely).
I absolutely love my G2's and would not trade them for any stock, even if the G3's were exact copies, in my hands and ready to go. I personally do not think the G2 needed slimming down, but then again I am not one to complain about weight issues. I just carry the thing. If it's too heavy for a purpose, I will use a lighter rifle.