Warning: The OM-D E-M1 is not for the feint of heart. It takes excellent photos when it does what I expect, which isn't all the time. The controls have a steep learning curve, which I haven't climbed yet. I'm going to give it five stars on the assumption that I'll climb that mountain.
• Takes great photos, if you know what you're doing.
• Battery let's you take at least 300 photos per charge, even with some flash.
• Fast shutter delay; very responsive (even if you don't want it to be).
• Can change settings on the fly quickly, if you know what you're doing.
• Six-hour sleep; you don't have to turn the camera off most of the time.
• iPad/Smartphone app works pretty well via WiFi, if you know what you're doing
• Olympus tech support is excellent.
• Lightweight and strong, even with a lens attached, with an easy grip.
• LED screen is very good and shows a greed deal of information.
• Viewfinder is excellent.
• Steep learning curve. Even on "auto" you have to know a little about the controls.
• Buttons are so sensitive that you can easily change settings or take unwanted photos.
• Included added flash is only okay.
• Lens designed to be bundled with this camera isn't out as of this writing (10/8/13) and will be pricey.
I've had the camera for a week, and have taken several hundred photos (look for me on Facebook), so feel I can comment, from a mid-level user's perspective. Most cameras I've owned have powerful controls, but if you just want to set it to "Auto" and take pics, a beginner can do it. Not so this camera.
The default settings for the OMD1 (how I tend to refer to it) are for the high-end user… with some odd exceptions. The arrow buttons change the focus. This is incredibly annoying, given how sensitive the buttons are, and if you don't pay attention the focus point will be waaaay off very easily. You can change how the arrow buttons work, but that reduces a great deal of the ease of the Live Screen controls. There is no command to lock the focus. Meanwhile, the default for the lever is "off". If you want to use the AF or HDR buttons to change the flash settings, you have to go into the menus and turn on the lever.
Most of the menu commands and settings have at least three ways of accessing them. This is good, as you'll probably want to turn off one or two. If you set it up right, one button gets you access to flash settings, HDR exposures, etc. The front and back dials give you control of two aspects on one screen. The touch screen commands take a delicate touch, but work well. I haven't even played with the function buttons yet.
The upside to the very sensitive controls: Almost no shutter delay. The OMD1 is very responsive. This is not always a good thing, if you happen to hit a button at the wrong time or chose the wrong setting by mistake. A little care is required.
Turning on the camera wakes it up quickly, but you don't even have to do that; "sleep"k kicks in after a minute (by default) and lasts 6 hours, so merely touching a button wakes it up. The battery has to handle a lot, but so far each charge has lasted over 300 shots. Haven't tried energy draining aspects like HDR combinations or RAW.
The manual is very good, and Olympus tech support is excellent (1-800-201-7766 press 1 (maybe))).
The viewfinder is great, though I usually use Live View.
Every now and then, the camera does something odd (such as take a photo for 2 seconds) that I didn't set up and don't quite understand why. I'm assuming that all will become clear in the fullness of time.
L SF (Large/Super Fine) .jpg compression puts it at resolution of 350 and smaller height x width, which means I have to massage the files in Photoshop more than I want to, even for simple Facebook uploads. This is the setting that gives the most info this side of RAW (according to tech support) and so what I, in theory, want. The extra steps in Photoshop are worth the results.
When the camera is doing what I expect, the images are excellent. Massaged in PS, they come out very nice. Sharp and clean.
The focusing works spectacularly well. I'm not sure how the AE works. It seems to be about a quarter f-stop off, at least for the people's faces when the background is lighter. I hope to figure out how to highlight the faces better.
WiFi connection via app to my iPad works, but is also non-intuitive. The app is brand new, just released, an update of a previous Olympus app. The connection, which should be simple, is handled strangely: The "Connection to Smartphone" is in a different menu than the settings for wifi connection, and you can't get out of the wifi screen when it's on. You either use the camera manually OR connect via WiFi. You have to change some settings on the iPad to connect and to allow access to the files on the camera.
So: final word, for now: An exceptionally good camera that takes great photos… when the symbiosis between photographer and equipment is complete. I do not yet grok the OMD1. I am going to give it five stars because the small camera takes great pictures. But please, note all the caveats.