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Seriously. If that's the case, it's crazy. Maybe we'll get half-life 1/2 and CS 1.6 on GoG someday.
There is at least one other Source game on GoG, and that's Vampire: The Masquerade - Bloodlines. They should really bring more Source engine games on here, like Dark Messiah, and obviously HL2 + Episodes, etc (and the HL1 trilogy for that matter)
Haha, that was my first thought as well, then I was reminded of VtMB. Still, we definitely need more!
If memory serves, Consortium was first.