The 19th November saw the 25th anniversary of Valve releasing what was and is a gaming masterpiece that really defined an age of 3d gaming and the move to dedicated 3d graphics cards. I remember playing this in software mode and then enabling 3d effects on my brand new 3dfx Voodoo 3 3500 gpu with a whopping 16mb of onboard memory and it was a game changer. The incredibly successful Half Life was followed up with a number of expansion packs and then the phenomenally impressive Half Life 2 that has to be on the list of the best games ever made.
Valve has a documentary with the development team to mark this milestone and if you are interested you can see it here