I think the biggest thing in this anniversary is not Half-Life 2 getting workshop support, nor Ravenholm getting some nice fog effects, nor the Episodes being integrated into HL2, and not even the new commentary nodes. I think it's at 1:46:23 in the documentary - Valve after almost 2 decades finally breaking the silence about EP3/HL3 and speaking about what happened to it, with some never-before-seen EP3/HL3 footage and concept art. Ice gun, Arkane Ravenholm game, it's even got the infamous blob NPC in action that we've seen mentioned in so many leaks!
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