Micro Four Thirds System
mFT cameras have taken the market by storm. I believe many photographers have seen the advantage this system gives without the bulk of the a DSLR. Using the same sensor as seen in the Panasonic and Olympus DSLRs, but utilising a smaller body because of a lack of a prism, gives excellent image quality and satisfies the requirements of 90% of photographers.
Certainly, a DSLR will be required for sport photography where fast autofocus is required. Low light photography is also another segment where these cameras do not excel. This is because of the way these system achieve focus. They use contrast detect (which eliminates the use of a prism), whereas DSLRs use the phase detect method.
I'm finding myself reaching more and more for this type camera when going out just because it's smaller and more convenient that a DSLR. This doesn't mean that I'm replacing my DSLR systems however, I just use them in places where a DSLR seems inappropriate.
With the introduction recently of the Olympus EM-5, E-M5 II, E-M1, E-M1 II and the E-M10 I & II I think the M43 system has finally grown up. These cameras are very very good. Focusing is practically instantaneous and the dynamic range has again been increased. The images also allow you to work them harder in post processing and banding seems to be less of a problem.
Not to be outdone, Panasonic cameras are no less capable os the Olympus although Panasonic have seem to have concentrated on video for their cameras. Certainly the GH4 was hailed as an excellent camera for video. The GH5 is expected shortly and I'm certain that will be a great camera for Panasonic.