Jason posted his first impressions story to Six Colors last week:
It’s a 5K iMac, albeit in a slightly darker shade. I made my transfer of data using Migration Assistant via Thunderbolt, which meant I needed to dig up a Thunderbolt 3 to Thunderbolt 2 adapter. (Turns out I had one of those!) I look forward to compressing more video and denoising more audio. This could be the beginning of a beautiful friendship.
I’ll say it again: I’m not in the market for this machine, but that space gray sure is pretty.