Take this with a grain of salt since I've only had my hands on this thing for a couple of days.
Coming from a Nikon and GF1 background, I was immediately struck by a few things:-
1. This thing looks really nice - black works for me. No paint flaking off anywhere, even with rubbing.
2. I miss the ISO and WB buttons. This is something I use quite a bit and I've had to map this to some buttons to get faster access to it and even then, it seems to take a step more for most things.
3. The thumb dial requires a little reaching compared to the GF1. Also, the GF1 thumb dial is clickable to make your selection. This allowed function switching with the dial (eg. changing from aperture adjustment to EV adjustment.)
4. I'm not sure if this is correct but the GF1 seems to have a start up time that's just a tad faster than the EM5. This is especially noticeable if the lens is not mounted. Even with the lens mounted, I found myself waiting a bit more. This may not seem like much but I was able to whip out the GF1 on a moment's notice to snap a shot.
5. The shutter release is further towards the middle of the body and also needs a bit more reach compared to the GF1 or Nikons. Having said that, the button does feel well built and rugged.
6. The FN2 button could be more responsive. I have had to press it all the way down and hold it to get the function. This could be a software design issue but it makes it feel less responsive the way it works now.
7. The four-way selector is a tad sensitive. I've overshot my selection several times, thus slowing down the usage.
8. This may be my coming from the GF1 but the menu system feels like it's not as intuitive. I've had to hunt for settings for a long time (for example to find the video focusing mode.) The GF1 menu system was more to the point it feels. Having said that, it does look nice on the screen.
9. It's nice that it has dedicated support for Eye-Fi.
10. It's really nice to be able to change the focus ring direction in the settings.
11. I'm still trying to get around some of the INFO screen system. With the GF1, I got everything on one screen. With the EM5, I had to cycle the screen with INFO button. Some stuff, such as battery level, shows up for a while and then disappears.
12. Speaking of the battery display, it's not very linear - it shows full for a long time and then tapers off real quick. Again, the GF1 seems to have found the right mix of information and simplicity so that I don't have to keep fiddling with the screen and get on with shooting.
13. I'm not sure about this one but there was an instance when I rotated the dial to open up the aperture and the camera didn't seem to want to open it up until several tries later. I'll need to verify this with more testing though.
14. Shooting at ISO1600 is no problem at all. If you're not careful, you may leave it in there without noticing.
15. 12MP to 16MP isn't that noticeable. Those of you with earlier generation M43s should not feel that you've been left behind.
These are some of my first impressions, FWIW. The video quality was better than that from the GF1 but seems to be still short of a good videocam such as the HFS-100. You gain lenses though, and DOF. Recorded audio is tinny but is fine for this type of device. I'll leave image comments to others as I've not had time to run it through all tests yet.
Daniel