I thought it was fine. Neither impressive nor underwhelming, but I've never paid attention to EVF specs. Again, what I saw was with pre-production firmware, so operation in the final version may be different. I use a Sony A7R and Fuji X-T1 (neither of which have a best-in-class EVF), and because I can use those just fine I imagine the X1D viewfinder will be just fine for my tastes too. It's definitely not the huge, bright, OVF of the H-series that I'm used to, but I'm happy to trade an OVF and the sub-par LCD of my old H4D-40 for compactness and an EVF with live-view and focus magnification. Despite any deficiencies in EVFs in general (blackout/lag/etc), I've grown to like them simply because they make checking focus/exposure MUCH easier in bright sunlight...no more squinting at a glare-y LCD and a higher rate of nailed focus captures for me.
I finally put my $$ where my mouth is and placed my X1D order yesterday. Now the wait.....