I’m an EM5 owner so I won’t comment on the EM1 IQ, but it does use an upgraded CMOS sensor which should resolve better IQ. Some people say the difference is negligible, some say it’s a worthy upgrade. The EM1 does offer more focus points vs the EM5 (81 vs 35) and it does offer WiFi, a feature I wish the original EM5 had, as that opens it up not only to easier transferring of images for sharing, but also remote shooting on iOS and Android.
For a more detailed breakdown, let’s checkout the chart from Amazon: