Hi rone,
For video I love the GH4 the form factor love the lenses I’m fortunate enough to have an uncle who used to be in the trade and over the years gathered a nice collection of Leica glass.
I cannot personally see any difference between between the Panasonic f2.8 glass and the Leica stuff I tested it against.
For stills (I think I maybe one of the few person who actually uses the GH4 for stills as well) It’s ok ISO wise I compare it to the Canon DIGIC 4 sensor.
For shooting stills in sport the lag in the view finder is a bitch, I could never use it professionally for stills of fast live action.
Overall it’s a great camera for video not the best for stills but its a compromise I made in not lugging two camera systems around with me. 🙂