Half-Life Blue Shift
This really was the one that got me into Valve stuff, but not in the way you'd expect. I didnt get intrested through playing the game (my shitty chromebook made sure of that) or even watching gameplay videos. I got interested through SFM/Gmod videos. Since I always have loved animation, they easily caught my attention. The really good sfms, like Lil Gaurdian Pyro and End of the line (links below) were the stepping off point into the weird stuff, like ancient shitposts and TF2 Freaks. The already absolute insanity of the lore of this universe and the absolute masterpieces of sentence mixing combined with the absolute creativity of humanity got me sucked down the rabbithole faster than a Scout on Bonk! All with never even touching a game.
Lil Guardian Pyro
End of The Line
I got into Portal basically the same as TF2, but I was more drawn to the music, Still Alive and Want You Gone. I also just really liked the concept of a Portal Gun, imagine being able to travel to a distant (but still within range) area in an instant! I also know, from what little I have seen around the internet, that this game is Really Funny.
Still Alive
Want You Gone
Half life/HLVRAI:
There was something sappy written here that is no longer true. Nothing lasts forever I suppose...
RTVS Twitch Link
(this is a joke.)