I love my olympus OM-D. The new upgraded and slightly more expensive version has a different layout and I'm not sure which of the two I would get if buying it now. I'd have to put my hands on the new camera.
But I love the older version.
Great image stabilization. I was using it handheld in dark churches in Eastern Europe and got great shots.
At high ISO it is somewhat noisy and nowhere near as good as my D4, but it is still quite usable at ISO 20000
At ISO 1600 or below it is very good.
I've used it with the new 75-300 mm lens which gives an effective focal length of 600mm and I have photos with great detail.
Of course I shoot only RAW
Here are some examples:
BIG HORN SHEEP - GLACIER NATIONAL PARK
HAND HELD FOCAL LENGTH 600MM F6.7 1/500 ISO 1250
ON TRIPOD FOCAL LENGTH 56MM F16 13 SECONDS ISO 250
HAND HELD FOCAL LENGTH 96MM F11 1/40 ISO 640
SALT MINES, POLAND
HAND HELD FOCAL LENGTH 60MM F8 1/30 ISO 20000