GH3 "new 16MP multi-aspect ratio sensor"

When shooting 16:9 or 3:3 this increases the crop and gives a smaller sensor

And better technology can offset having a smaller sensor, but you also need a different lens.

A lens that would capture the image on a GH2 will not capture the same image on a GH3 so to even make the comparison you may even need a different lens. That is where the real headache arrives.