These are expensive cameras, there's no doubt about it.
I loved my e-p3, it's been through the wars and come back fighting, I'm just an amateur, but I've won a good award with the e-p3 and sold the prize to get this upgrade. I'm not disappointed.
Main points for me / basically differences:
The tilting screen is nice, personally I was happier before as I worry it might just be another thing to break, and bomb proof is more important to me than a tilting screen, it also doesn't feel quite as sensitive. But it's bright and fine and the hinge is well made, not flimsy at all. I have no complaints.
The body is pretty much the same size as the e-p3 so with a pancake you can squeeze it in your back jeans pocket. It's tight, but ok enough that I do it regularly.
Silver version is prettier, probably a bad thing as you don't want to 'care' too much about getting your camera bashed.
Live exposure is great, not a gimmick. For long exposures it's useful, I don't do light painting, but I'm sure it'd be great for that too.
Wireless connectivity is more useful that I thought.
There's definitely a difference with the new sensor.
Stabilisation on video basically works now. E-p3 was terrible.
I don't have a problem with the video, I've used it for a few things and have no complaints, that said I've never used anything else so don't have anything to compare it to and I know that people prefer lower fps which isn't in there. Read about this if it's important to you.
I've not had it long, so there are no doubt going to be draw backs and failings that I've not spotted, and plus points I've not come to appreciate yet.
In summary though, if you can afford it, this is the most amazing bit of kit. I've loved my e-p3 and the e-p5 is off to a flying start.