Just a quick look at a casual comparison between a full-frame DSLR known for its high-ISO performance with a new, high-quality prime lens on it – and a Micro-Four-Thirds Camera with a decent prime lens.
What I saw was expected, and unexpected. I >did< expect to see a big difference in the depth-of-field – bigger the sensor, more shallow the d.o.f., and that was visible. I intentionally shot at a higher ISO, with each lens wide open, and was pleasantly surprised at how well the MFT camera’s file looks. I expected more noise/grain, but it seems comparable, if different, to the FF DSLR.
Oly on the left, Nikon on the right; full-view on left, 100% on right.