Panasonic seem to be getting better and better - the latest sensor Pana made is the one in the OM-1.
Panasonic makes some killer equipment, the gh3 and i'm sure the gh4.
In regards to the em-1 that uses the pana sensor vs. the em-5 that uses the sony sensor, it may or may not be the sensor, but I've shot those camera side by side a lot and the em-1 is 10 times the camera of the em-5 but the look of the em-5 is just beautiful.
I hate this term, but the em-5 is film like and the em-1 a little more technical.
We even tested them next to the p30+ and the Leica S2 with flash and the em-1 held up amazingly well in detial, though the em-5 still was the prettier file.
But don't knock the pansonic gh3 camera because it may be non pretty as far as cameras go, but it's the most intuitive electronic camera made, the menu is a snap, the function buttons are very easy, very smart and it shoots a hell of a video file.
IMO
BC