I think it is pretty good - much better than the EVF in the X100S I tried, the main difference being the refresh rate is significantly higher and doesn't degrade nearly as quickly in low light. I think from a size, color and resolution standpoint it is excellent. It still stutters at times and a friend of mine who tried one sent it back, saying he couldn't stand the "tearing". Of course he is happy with the EVF in the Panasonic GX7 I sold him and I thought its EVF was pants compared to the X-E2
The Olympus E-M1 and VF-4 accessory are probably as good as it gets right now. I think the X-E2 is a little sharper/contrastier, but the refresh rate is more consistent on the Oly.
If the X-Pro1 is anything like the X100S, this is a huge improvement IMHO.