Personally I feel Frogger pioneered violent video games, so maybe we should be giving credit to it.
I got into Half-Life when I got kind of pissed off when Counter-Strike didn’t have some sort of campaign to play. Course, I was just a kid back then and I thought CS was the base for Half-Life when we all know that it’s the other way around.
That first zombie in the game just scared the hell out of me and I didn’t play HL again for a few months afterwards. 
If I recall, the first mention of a violent video game would be Death Race in the arcade. Of course, a lot will agree that the likes of Wolf3D, Doom, and Quake just pushed the FPS genre to mainstream, but of course they are not the first with such ideas. You could even agree that without those games, the likes of 3Dfx and the graphics card race might not have even happened. Damn do I feel old already. 8|
First FPS was Maze War from 1974. It gave you points for shooting each other in a maze. Either that or some game called Spasim, and while it was first person, it was a space shooter.
For some reason, I have a really fond memory of fighting the Nihilanth in GoldSrc Half-Life. It took me an hour to actually beat him, and while I was fighting, I was also talking to my then-best friend over Skype and all-in-all I was having a heck of a time.
Also playing Half-Life’s multiplayer on an oddly active server (considering it was like, 2013) was really fun. I’ve always loved ratmaps, and this server had a rotation of them. I remember playing CS: Condition Zero when I was like, 11, in a game shop, driving around in a giant pencil car. It was a fun time. I’m glad that I’m able to appreciate older games like that despite mostly growing up with the Gamecube and Wii.
If HL2 counts too, I have a really strange one.
I was sick with an awful flu, and had a nasty sore throat. So to pass the time, I was playing Half-Life 2 while drinking a warm drink, and for some reason, the memory of fighting the Hunter Chopper in Route Kanal and making my way down to Black Mesa East really sticks in my mind. Despite being sick, i really enjoyed that night. I don’t know why, but I always have the most vivid memories from when I’m sick.
All-in-all I’d say Half-Life has had a super positive impact on my life.
Statistically, if you randomly encounter someone playing Half-Life, there’s a 65% chance they are probably working through On A Rail.
What’s the statistics behind encountering someone playing Half Life tho, that’s the question.
50%
Pretty slim unless you happen to be in the same room with them while they’re playing it
My fondest Half-Life memory has always been the eerie green glow of the radioactive goo in Blast Pit.
Finally figuring out “On a Rail” and then going through and killing every marine and getting every health and ammo pack after numerous deaths