I'm not a fan of the "micro-four-thirds" sensor size. You see, cameras are devolving, and we are constantly choosing convenience over quality. I'm not saying that size and weight don't matter, because they do. What I'm saying is that image quality also matters (vision matters most).
At one time what we now call large format was the standard format, but the cameras were large, heavy and expensive. Then came medium format, which was much more convenient, but not quite the same quality as large format. After that many photographers switched to 35mm (what we now call "full frame"). Kodak tried hard to push the APS size in the 1990's. Micro-four-thirds is even smaller than that.
I personally have drawn a line at the APS-C size, which is just barely large enough for my tastes. Micro-four-thirds is simply too small.
Why does size matter? Because not all pixels are the same size. In order for Panasonic to squeeze 16 megapixels onto their tiny sensor, they have to use smaller light sensors, which are not as sensitive to light (especially dim light) as larger pixels. In other words, 16 megapixels on a micro-four-thirds sensor is not the same as 16 megapixels on an APS-C sensor, which is not the same as 16 megapixels on a full-frame sensor. Specifically, the differences are most noticeable in dynamic range and high ISO.
With all of that said, the Panasonic Lumix DMC-GX7, which is a compact interchangeable-lens micro-four-thirds camera, gets pretty darn close to APS-C quality. In fact, DxOMark ranks it right up there with many APS-C cameras.
In other words, this Panasonic camera blurs the line that I have drawn on sensor sizes.
The problems that I see with the Lumix DMC-GX7, however, are that it is priced too high (you can get a similar Sony or Samsung camera with an APS-C sized sensor for the same price) and that it isn't significantly smaller or lighter than other compact interchangeable-lens cameras. What is the point of micro-four-thirds if it is not cheaper, smaller and lighter?
I think Panasonic is on the right track with the micro-four-thirds cameras, but they should not forget why people choose that sensor size.