I quite liked the previous generation of EVFs and the latest ones I've used, in the Sony A7 and my own Olympus EM1, are good enough that I generally prefer them to optical viewfinders, even big, bright ones like I had in my old E3. They are certainly better in low light.
However, today, I noticed at least one limitation. Shooting a dotterel in rocks in bright sunshine, the contrast was too high and the pattern on the dotterel merged so well with the rocks that I had to use my eyes to work out where the bird was. In that situation, the EVF is not "there yet". I also tried tracking flying swallows, a bit of a torture test, and the high contrast in the bright light also made things less easy there. However, any viewfinder is a challenge trying to chase swallows!
Oddly, I can change the brightness and white balance in the EVF but not the contrast. To be fair, it is usually so "right" that it is easy to forget it is electronic. It's just really bright sunshine and a contrasty background that is the problem. Not that common a scenario so far this summer...