After having the E-P1 a day, I can confirm that the camera is exactly as expected. It has the image quality of a (low level) SLR, and the focus performance of a (high level) compact.
Image quality first. It simply blows away cameras such as the Panasonic LX3 or Canon G10. It can resolve fine details that simply aren’t there with smaller cameras, and even if I haven’t stress-tested it yet, it does appear to get a resonable amount of dynamic range out of tough situations.
Noise performance at ISO 1600 is perfectly acceptable. Auto ISO works brilliantly in P and A mode, choosing more or less exactly the same ISO setting (between 200-1600 by default) as I would myself, if I tweaked it in 1/3rd stop intervals between every frame… In iAuto mode, however, Auto ISO makes so weird choices (often pegging the ISO at 200 even in low light) that I’m inclined to think it’s a firmware bug.
ISO up to perhaps 3200 can be used in really unfortunate situations in order to get a picture that would otherwise be missed, but noise starts to get very annoying in that case.
In other words, exactly what one would expect from a (relatively) large sensor.
When it comes to focus, in good light (outdoors or indoors during daytime) it’s fast, in bad light it’s sometimes painfully slow, but as long as the subjects are stationary it does tend to be quite accurate when it finally acquires focus. If you want to shoot animals or kids running around indoors, this is absolutely not the right camera for you.
In other words, exactly what one would expect from a contrast-detect focus system. Accurate and fast focus of moving objects in low light is still entirely the province of DSLRs.
Compared to my 20D (with grip and a reasonable lens), it’s a joy to run around with however, it’s small and weighs almost nothing at all, and can be thrown in any small bag. It’s not quite go-anywhere since it won’t just slide into a jeans pocket, but it’s absolutely go-most-places.
Also, everyone I’ve showed it to thinks it’s a really handsome camera. That may not help the quality of my pictures, but it sure feels good. 🙂