"If you're absolutely unwilling to compromise on image quality then spending twice the money and moving up to the bulk of a full-frame is the only way of gaining a significant step up from the E-M5."
I never had any doubts about the usability of the OM-D. After the first half-hour I spent with it, I knew that it had all the speed and functionality I needed. It handles very nicely as is, and having spent some time with a model that had the grip(s) attached I know that will work well also. (My grips are arriving sometime in the next 28 days, so I'll do some pieces on that obviously.)
My initial reservation was about the high ISO jpgs. and I still think they are pretty unpleasant at 3200 and above. The smearing of detail makes them virtually unusable to me. However, as usually happens, Adobe Camera Raw support changes a few things. I was, though, surprised at just how good I could get files shot at ISO 3200 and 6400. For a micro-thirds camera this is definitely a step forward and also an encouraging one for fans of the system, since Panasonic are now obliged to equal this.
The other bugbear of m4/3, restricted dynamic range, has also improved significantly with the OM-D, and shows just how far in-camera software and processing has come. With the OM-D the notion of having to compromise somewhat on image quality to use the system has largely disappeared. All my "fixes" that I came up with to allow me to use m4/3 for my work are mostly unnecessary with this new Olympus and the raw files are a real treat to process and view.
One of the things I always look at is how far I can upsize an image, as that is important for my stock photography work. Now with Photoshop support I have no problem interpolating the OM-D files to the same size as those produced by my Sony NEX-7, assuming that I use a decent lens and get the exposure right. It is very difficult to see the difference between a NEX-7 and an OM-D upsized file and I have uploaded a few and had them accepted already.
I would however make the point about decent lenses. The better the sensor, the more I can see the differences between lenses. I'm putting together a post about the 12-50mm zoom, which should appear after this one. Used on a tripod at optimum apertures and with the subject matter relatively large in the frame, it can do a good job. However, under what might be described as my "normal" shooting conditions, I am somewhat disappointed with it, in terms of sharpness. Certainly the 12mm, 45mm Olympus and 20mm Panasonic lenses I have do a much better job and produce beautifully sharp files. And of course my m-mount Voigtlander and Nikon primes do much the same. All I would say, is be wary of the kit lens(es) and if thats what you start with added to the OM-D, then I would suggest that you are not seeing it at its best. I would also say that only shooting jpgs. is also failing to realise the potential that the camera has.
So all in all, an excellent camera, and one thats going to make a lot of photographers, and, I suspect, a lot of other camera manufacturers sit up and take notice.
For my part, this is exactly how I want to see m4/3 progress. Leave point and shoot to somebody else, and the mobile phone companies. This is a camera for serious photographers who want a versatile, well built and designed quality tool. If the NEX-5n was my camera of 2011, then this is most definitely my camera of 2012. And one thing I know for sure, is that I won't be the only person who thinks that.