A very comprehensive review as always from Dp Review. Some interesting points made throughout it and the conclusions are surprisingly complex. For example, while they say:
Overall, this is the best image quality we've ever seen. Which is what you'd hope for, given it's one of the most expensive cameras we've ever reviewed.
They also point out...
And though it does offer the best combo of dynamic range, resolution and noise performance of any camera on the market, it only beats its full frame competition by a small amount. The Nikon D810, Pentax K-1, Canon 5DS R and Sony a7R II all offer 90% or more of what the Fujifilm offers in terms of IQ, at a substantially lower price and weight, with a far more versatile lens selection that, at times, allows these systems to overtake the GFX in terms of low light performance and subject isolation (shallow DOF).
Overall they gave it 85% and a gold rating. It's well worth a read if you're interested in this camera.