chuckd on 16 March 2008
I haven't played HL1 in a long time, but when it came out, it really revolutionized the fps genre. It had the best story (well, most fps' at the time really didn't have much of a story) and the most varied gameplay, but it's most influential trait was the adaptive ai. Everyone does it now, but Valve did it first.
Also, the sdk led to a plethora of really awesome mods. CS, TFC, DoD just to name a few. I spent $30 for an awesome game and got about 1000 hours of play out of it.
