The linked related discussion is being tracked at https://github.com/ValveSoftware/Source-1-Games/issues/1841.
I can confirm the issue was because of ati-drivers version.
14.6_beta2 vs 14.9
After installing 14.6_beta2 back DOTA2/CS:GO got back working.
(I also updated xorg-server from 1.15.0 to 1.15.2 [~amd64], but don't think it's related).
oops.
Closing as this issue appears to have been resolved shortly after it was reported in 2014 (per discussion on https://github.com/ValveSoftware/Source-1-Games/issues/1841) and general video driver quality from 2014 is no longer relevant.
Nothing extracted yet.
Hay, I'm running Steam on Gentoo GNU/Linux.
Just updated my 'ati-drivers' package to latest 14.9.
Now both my DOTA2 and CS:GO stopped working properly.
I see a "black screen", I hear DOTA/CS loading sounds, but after that nothing happens.
To check the issue I downloaded Borderlands 2 and couple of more games, they all seemed to work fine with OpenGL rendering n' all.
I also found this related discussion on the forums.
Here's the details of 'lspci' command:
Everything did work fine with 14.6_beta2 drivers.
This might be a Source engine issue.