I use a 70D with L lens for serious photography. The problem is the camera, lens, filters and tripod weigh 6.5 kg. For mountaineering and occasional use I have had a G10 since it came out. This is good at base ISO, then noise is the name of the game. I bought the G5X because it has a much larger sensor and a viewfinder. A camera without a viewfinder is useless outdoors.
As stated elsewhere the G5X is beautifully built and I find it has sufficient direct controls for ease of use (it does have a 200-page manual, though). I cary my cameras on a strap around my neck to avoid dripping them (and so I can grab it and take a picture one handed when mountaineering), so the size I find fine. In fact the G5X fits in the same case as the G10. So far I have confirmed that the this camera is useable at much higher ISO values than the G10, and using the protection against over or under exposure of bright or dark areas maintains detail, although I have not yet made test with and without these features.
I much prefer an optical viewfinder, but the electronic version in the G5X is useable even in bright light and removes the "hit and miss" effect when no viewfinder is available. I shall need to make more tests, but image quality seems good, although not comparable with my DSLR kit.
The only real criticism is the battery, which ran out on me in the middle of my grandson's 5th birthday party. This issue has been mentioned by other commentators and it is clear that it is essential by purchase a spare battery, even for a single day's shooting. The screen and electronic viewfinder use power in a way that a DSLR with an optical viewfinder do not.…mehr