I can only think of three games of recommendation honestly.
Otherwise never clicked with the Half Life game I played (HL2) or gave me interest to dive in more, I respect the quality (A.I. is certainly not as good as fans claim though). Perhaps my biggest gripe is finding the method of storytelling in HL2 to be a clutch on modern gaming. I played the D00M series the same year, and outside D00M III, a much more appealing shooter over Half Life 2.
And honestly not much else worth mentioning from Valve. I don't think they're this pillar of greatness some have made them out to be.
Valve hire developers, to work on sequels just to fire them mid-development and take the credit for that hard work (Turtle Rock Studios and IceFrog). Classy_
Only reason DotA2 is even remotely popular is because the original mod defined a genre. And even then League has made DotA2 pretty irrelevant.
Lastly- Counter-Strike: GO is good on the surface till one realises it's designed for idiots and kids to gamble over skins. Yippe
At least that TF2 and Portal games, am I right? . .
@RSM-HQ: You know, despite the fact that I played DotA from 10 years old. Now the young guys are not attached to that atmosphere of the first bunker. But, she is now probably the most popular game and prize pools show it.