Oh, blimey, I was not using NVIDIA drivers. Sorry for the invalid report, it's a bit late here, I changed to NVIDIA drivers now.
If the game runs properly after it has finished downloading again, I will close the issue.
Any luck? For what it's worth, this belongs over on https://github.com/ValveSoftware/Source-1-Games
Still downloading, needs another 20-30 minutes. As soon as it finishes I'll update the issue accordingly.
For what it's worth, this belongs over on https://github.com/ValveSoftware/Source-1-Games
Blimey. I should not be posting reports at 5AM ever again.
As expected, it was a driver issue. Game runs ok with NVIDIA driver, issue closed.
Nothing extracted yet.
I tried thrice to run Portal (Beta) by pressing "Play" in the Steam Library after it finished downloading and it got stuck in a black screen.
My system information:
Processor Information:
Operating System Version:
Video Card:
Sound card:
Memory:
Miscellaneous:
P.S. Out of curiosity I checked the integrity of the game's cache, and every single file failed to pass. As a result, Steam is downloading the whole game again right now.