Добавил: The DSystem
Inspired by the beta version of Opposing Force. All Grunts replaced by their counterparts from Half-Life.
1 - Extract the folders with "_addon" on the Half-Life folder.
(Example: C: \ Program Files (x86) \ Steam \ steamapps \ common \ Half-Life)
2 - Once the game starts, check the options, and in the video tab check "Allow custom addon content."