I got mine on release day and gave it a little run yesterday.
1) WIRED NETWORKING. You'd have to live in the country with 802.11ac wireless before it would be worth trying wireless. Apparently power line networking works well, but not in this old apartment, I'm sure.
2) Windows. Yes it kinda works on Mac, but it also kinda doesn't scale resolutions and it also kinda freezes in the middle of a game. I will give it time.
If you have those, it actually works really well. I played Toybox Turbos and Tomb Raider Anniversary on it yesterday, it was fantastic.
I haven't aggressively tried non-Steam (i.e. GOG) games yet, though I don't see any huge issues with ones that run directly. I couldn't get Minecraft to run nicely when launched through MultiMC (for my mods), but I haven't come to the end of my efforts yet.
I'm happy. The controller is great too. It would be awesome for most (if not all) GOG games too, since the majority won't have Xbox 360 controller support built in. It's crazy configurable.