Portal 1 & 2, Half Life 1 & 2, Dota 2, Team Fortress 2 & Left 4 Dead (And Counterstrike & Artifact and a couple VR games) But for a big video game company, that's not a lot. Especially being as thats the last 20 years. Nintendo releases almost twice that per year, but Valve is definitely a quality over quantity, as almost all of their games are masterpieces, and Valve is a LEGEND cause their games are almost always on a huge sale on their marketplace, Steam. And again, unlike Ubisoft, who has huge sales all the time, Valve's games are actually good, and if you think Ubisoft is good, Valve is that much better