DP Review has posted the most in-depth "preview" of a camera that I've ever seen.
The part that interests me the most, though, is the photographic tests section, which they have posted for JPEG. It's here that the quality of the new/kinda'-new sensor will be revealed. And what a revelation it is! There's little perceptible difference between the E-P3 and the E-P2. At low-ISO, they are, for all intents and purposes, identical. And importantly, it's here that the extra four megapixels of the Panasonic G3 come to bear, with the G3 noticeably out-resolving the E-P3 in many areas of high-frequency detail. There are even a few areas, such as the spools of thread, where it appears that the JPEG processing of the E-P2 is actually doing a better job than the new E-P3.
Now change over to the E-PL2 and Panasonic GH2.
Even at this low-ISO, the cameras are all showing noise in their JPEG output. The E-P3 appears to be most aggressive with chroma noise reduction, and as such its dark-grey areas are the least affected by color blotching. In general, I'd say that the GH2 has the best JPEGs.
Move the ISO up to 1600, where most 4/3's cameras usually start to fall on their faces, and the new E-P3 is definitely outperforming the old E-PL2. This benefit appears to be primarily in shadow areas, which is great, and I'd say it's somewhere over a half-stop improvement. Of most interest, though, is that the new E-P3 is showing much better saturation retention, and color is always more important than detail. Crucially, though, the camera is still being noticeably beaten by both the GH2 and the G3. Moving the ISO up to 3200 only amplifies these distinctions, but it does reveal the stronger default noise-reduction of the E-P3.
Again, I remain unimpressed. Many functional issues have been addressed, which is great, and if this had been released as the very first Pen camera, I would have called it a masterpiece. But it's not the first Pen camera. This is two years later, and Olympus still lags behind the competition.
If Olympus really wants to disrupt the market, leave Panasonic, get in bed with Sony, and start using a goddamn up-to-date sensor.