Size & Feel/ build - It is very small, even smaller than the GRII, but only just. It *feels* like it is made with less quality materials, but seems to be fairly sturdy in real use. The overall build quality is not great, the screen comes out over the side of the body, meaning it is not flush like the GRII.
Quality of photos - 24mp - Resolution is where the GRIII trumps the GRII. The extra megapixels allow for any cropping that might be needed, but also is one of the only things that feels like a proper upgrade over the GRII. The quality of the photos is exactly what I want and expected, which is the look and feel of the GRII but has extra megapixels. There is a little bit of CA I have noticed for objects far away when at F11, however, this is not a really an issue for me, but will bug pixel peepers/
Macro function - The macro function is brilliant. Along with the upgrade in resolution, this is one of the saving graces of the GRIII. The F2.8 allows enough DOF separation, especially when outside. Images are sharp, and it does a better job than the GRII.
Auto focus - The Autofocus is improved over GRII, however it is still slow by todays standards. This is another thing that does not bother me, as I tend to use SNAP focus more than anything. This is something that could be upgraded with a firmware update anyway...
IS - The Is is a handy feature, and you see more and more brands adding IS, and it is useful, but feels like a first attempt at IS.
Menu - the menu is convoluted and less simple and functional that on the GRII. They have thrown in Bluetooth and WiFi and a few other gimmicks which feels like a step away from what the GR series should be about. A lot of functions can be moved, which is cool.
ISO/ EV lever - The most important thing about the GRII P mode was the level controlling the ISO at a quick flick of the finger. There may be a away to set this, but I have had no luck so far.
Rotation/ circle lever- a cool feature, but pointless if you are throwing in a touch screen. However, I use the wheel more than touch screen.
Touch screen - Just another gimmick to go in the little box, and another potential to go wrong. Touch screens can be and can become not very user friendly, however it is certainly functional in the GRIII. I turn it off, but there will be people that like this sort of thing.
Battery Life - about 3 hours shooting with camera on all the time walking the streets. Not too shabby, and I expect all the little new extra things drain the battery like nobodies business. I always recommend getting a second battery. It also does not take same battery as GRII, so you cannot transfer this.