Futhem and their new engine craps.
That will probably be a new dark era....
I'm too lazy to resume the article in depth, but;
¯, , , ¯¯,¯, , ,, , , ¯¯ ¯¯¯¯ ,,, , , , , , , ,,,, ¯, , , , ,,,,,¯¯,¯Counter-Strike: Source, Day of Defeat: Source, Half-Life 2: Deathmatch, and Team Fortress 2 will soon traverse over to the steamapps/common section of your Steam folder instead of the older steamapps/[username] destination. The conversion is automatic: Valve says you’ll need enough disk space “for about two full copies of the game” as it changes over.
Backup your stuff just in case.