Final "initial" thoughts...
First, the caveat that this is based on a pre-production unit of the Olympus OM-D E-M5. Often, these are still to be optimized, which can be done through firmware updates, and the finishing may not be up to full production specifications yet. With this in mind...
Design – the design of the OM-D is likely what has drawn the most attention to the E-M5. Its retro styling, available in both black and silver, brings back memories the old OM SLR-stylings. The mode selector has been relocated to the far side of the body, allowing for the rear and front dials thumb and finger dials, similar to that provided in higher-end DSLRs. The same 2 fingers can also conveniently access the movie record, review, Fn1 and Fn2 buttons. The 4-way button as well as the review and Fn2 buttons appeared a little soft on the pre-production unit, but hopefully that'll be fixed up together with the waterproofing on the production units.
LCD and EVF – The tilt 3” OLED rear LCD is great, which also incorporates touchscreen focusing point shooting. However, I did not like that the LCD was suppose to be pulled out from the top, implication of which is that in order to tilt it upwards, you are suppose to pull it out from the top first, then pull the bottom for it to face upwards. Yes, you can tilt it upwards by directly pulling out the bottom, but it's slightly harder as the mechanics of it is not designed that way. The 1.44M dot EVF boast a high refresh rate, and while the resolution is good with customizable display, I still found it to lag ever so slightly. But this is more obviously when taking pictures of moving objects, e.g. kids.
5-axis IS and AF – To me, the in-camera image stabilizer is the largest plus point for the E-M5, and the Olympus M43 bodies in general. Many would find this feature useful, from mounting native Olympus M.Zuiko lenses, to other M43 native lenses, and lenses of other mounts via adaptors. The AF is fast, as advertised... while not proven via an AF faceoff. While face detection is not for everyone, the availability of a well implemented face detection option (with left-eye, right-eye, or intelligent priority) is also good to have. Incidentally, the improved 3D AF tracking should help "track" down some of those kids shots...
ISO performance – Again, the caveat that this based on a pre-production firmware, but one can imagine that there can only be upside to the results here. Mind you, what is “acceptable” varies from individual to individual, but results show good high ISO performance all the up to ISO1600-ISO3200. But there'll inevitably be the lost of some micro detail and contrast, but the images still look pretty clean and useable.
The direct comparisons will likely be the Panasonic GX1 and possibly the Fujifilm Xpro-1 (although the price points are quite different), each of which brings something different to the table. But the E-M5 does make a strong case with its 16MP Live MOS sensor, new TruePic VI image processor, high ISO performance, 5-axis (in-body) IS, dustproof and splashproof-ability, compatibility with a large array of lenses (some via adaptors), and its retro-stylings.
A final note, while the Olympus E-M5 has pretty much matched the Olympus E-5 in terms of image performance, I look forward to more to the M43 lineup from Olympus. Further, I can't wait to see how this camera paired with the rumoured M.Zuiko 75mm f1.8. This continues the build on the 12mm and 45mm towards a strong M.Zuiko lineup of prime lenses. I eagerly hope for and wait for developments of a fast 17mm and a 25mm (roughly 35mm and 50mm on 35mm equivalent) to the line-up.