Nov 2018 - Artifact (Collectible card game on Windows/Linux/MacOS)
Apr 2016 - The Lab (Windows only)
Dec 2014 - Left 4 Dead: Survivors (Arcade game?)
Oct 2014 - Counter-Strike Nexon: Zombies (Windows only)
2013 - Counter-Strike Online 2 (Windows only)
Heck even their new tentpole title Half-Life: Alyx is Windows only. Those aren't really big Linux credentials to boast about.
I’m 100% not complaining because Proton has enabled me to play a libraries worth of games that were previously unavailable but it’s not exactly a victory Linux. The future might look like devs testing a little bit in Proton as “Linux support.”
While it is an admission Linux gaming was hardly going to take off on its own from a cold start, it allows people to use the platform that makes more sense for them. With the increased capability of Linux+Proton as a platform, its horizons are pushed and it makes more sense for more people.
The only possible downside here is the potential for a developer to neglect Linux support now that people "can just run it in proton", netting Linux users a couple losses of what-would-have-been native ports. However, I believe the increase to the viability of Linux gaming overall makes up for it.
Half-Life Alyx is coming in 2020.
The meme that Valve doesn't make games isn't real.
Even to hold people over they could have resurrected HL:DM and made it F2P.
So sure, Alyx is coming. But before that is a six and a half year gap in major games.
And if you discount CS:GO and Dota 2 as remakes, then you're looking at Portal 2 all the way back in 2011.
All source games work on linux, but the new half life game might be the first exception. Proton works pretty well for other games, but there are hard blockers on some (for ex: the anticheat in pubg)