Going a step aside from the technology itself, here's another way of looking at those games:
Half-life basically helped kick start story-driven FPS games (Bioshock, etc)
Half-Life 2 helped kick off physics based FPS games.
Portal basically kicked off the FPS puzzle genre (Talos Principle, QUBE, Quantum Conundrum, etc).
L4D basically kicked off FPS co-op games (Borderlands, Killing Floor, PayDay), as well as asymmetric co-op.
For better or worse, TF2 with hats and later CSGO basically started the microtransaction/crate system.
Lastly, Dota 2 did a lot to push e-sports forward too.
This is the kind of advances Valve is interested in. It's hard to tell now, but this game could easily have a huge impact on how VR games are made in the future.
Half-life basically helped kick start story-driven FPS games (Bioshock, etc)
Half-Life 2 helped kick off physics based FPS games.
Portal basically kicked off the FPS puzzle genre (Talos Principle, QUBE, Quantum Conundrum, etc).
L4D basically kicked off FPS co-op games (Borderlands, Killing Floor, PayDay), as well as asymmetric co-op.
For better or worse, TF2 with hats and later CSGO basically started the microtransaction/crate system.
Lastly, Dota 2 did a lot to push e-sports forward too.
This is the kind of advances Valve is interested in. It's hard to tell now, but this game could easily have a huge impact on how VR games are made in the future.