So what is it? Mine is Portal 2 if you couldn’t already tell from the profile picture and background. It was the first game that introduced me to Valve and PC gaming as a whole. I originally owned it on the PlayStation 3, but as soon as I saw the trailer for the Perpetual Testing Initiative I was all in. 
Feel free to share any stories about your favorite Valve game! 
Counter-Strike: Source is my favourite Valve game for sure. I got it for Garry’s Mod and became addicted to their minigames servers and 35hp knife maps. I’ve met a bunch of people from these servers and we still all play CS:S together from time to time (none of us seem that excited for CS:GO). The game’s rules are so simple, people have made maps with mechanisms that do various things to make the game exciting and play with modified rules.
Of all the Valve games I’ve looked at the map editor for, CS:S has the most potential for creative minigames maps and the like. The game lets you use a flashlight, NV goggles, a variety of weapons that can be purchased from within a trigger volume (buyzone) or found on the map or given directly to any player. Weapons can be taken away also, and other variables such as player health, coordinates, size, speed, gravity, and basevelocity can be changed at will. Players and entities can be given targetnames so you can have VIP players who can trigger secret doors and you can even use Sourcemod to teleport Steam IDs to developer rooms, where other settings such as triggering music, screen overlays, color correction, picking specific maps and changing playermodel via map can be done. Of course, all this can be triggered automatically on map spawn (new round). You might even want to have the map do something different on the next round based on something that triggered in the previous round, that’s possible too! You can change player teams via map, add score to a player on the scoreboard via map, avoid placing spawn points for the other team to allow for the entire server to be on one team to make maps such as course maps, parent entities and brush entities to weapons like grenades, knives and terrorist C4s for trails and such that stick to the player who picks the weapon up, and even change player and entity RGBA for invisible or colored entities and players or maybe change the models of them, for custom grenades for example. It’s even possible to make a voting system for selecting options for a map. Don’t forget the game_ui entity which allows direct control input- you could make it so one team gets a speed and jump boost if they left click, for example. In addition, there are functional camera entities which can project what they see to a material in real time for security monitors, for example. Soundscapes let you use custom sound for rooms, which can be used for changing music as players walk through walls into different rooms with a suddenly different theme to them. Custom sounds and textures and models make custom maps so much better. I’ve also heard it’s possible to use vehicles in the game, but I’ve yet to verify that myself.
There’s just so much people have done with the tools given to them, and it’s one of the reasons I still play CS:S. At this point, I’ve become so used to the feel for CS:S that it’s difficult to imagine losing some of the most important features and being in a modified game engine in CS:GO.
Practically, I don’t know! But my favourite has to be Team Fortress 2. It was my first ever game on Steam.
I’ll be the odd kid and say Half life 1.
The game that changed the gaming industry
I’ll say Team Fortress 2, just because I played it way too much back in the days. While the standard game was plenty of fun, I also have fond memories of playing Prop Hunt, Zombie Fortress, and Parkour Fortress. In fact, Parkour Fortress is the mod I wrote my first Steam guide for (I eventually made one for Prop Hunt as well), so they’re the reason I’ve gotten into writing guides. Plus, TF2 was the game used for the PixelTail Developer Grudge Match, if anyone remembers that. I don’t play it anymore, but it was fun while I did.
Special shoutouts to Half-Life: Source (for being my experience of the original Half-Life story), Portal 1’s Advanced Test Chambers (for melting my brain), and CS:S (for being the game I bought back in 2011 to play with my friend. Lots of good, old memories of being terrible at that game).
Portal 2 c:
Gotta be the classics
Love me some Half-Life 1
Half-life 1 and Portal 2 are my favorites. I’d also put Sven co-op here, but that’s a mod.
Is there an all the above option? Lol.
I think “Portal 2”
Actually this is only valve game i ever played :I
By far,
Ricochet.
Half-life 2
Never played Half-Life so it’s gotta be Portal 2.
Probably either Portal or The Lab.
I would say Left 4 Dead 2