I am a G9 user, but haven't taken it underwater yet. My last underwater rig was a Nikon D200, and am now really comfortable with my G9 (topside), and am setting up my Nauticam rig. Hope to have it in the water in the coming weeks.
So my comparisons are really topside based, but I love the G9. It is a comfortable and fun camera to use. Intuitive to use and capable of a wide range of photos.
Looking forward to getting the unit underwater.