> no AAA stuff, but e.g. Cities Skylines and Portal 2 work flawlessly
Do you get playable frame rates? Cities: Skylines pretty quickly falls to 20-30 fps even with a recent Nvidia card with closed Windows drivers, wondering how is the experience with AMDGPU.
(Haven't tested OpenCL, multi-monitor and HDMI audio, though.)
So IMO, if your GPU is supported by the AMDGPU driver, by all means give it a try.