Brace yourselves, but we may never see Half-Life 3. We will, however, always have Half-Life 2—and, thanks to the efforts of a group of modders, it may soon be playable on current Oculus Rift and HTC Vive headsets. The Half-Life 2: VR mod that first saw the light of day back in 2013 has been resurrected on Steam Greenlight, with updates that will allow it to run on current VR hardware.
As explained by Road to VR, the original mod fell into disuse because Valve didn't update the Source engine to keep pace with changes in Rift and Vive headset software. Now, however, members of the original mod team, along with some new additions, have figured out how to make it work with current headsets, and also to support motion controllers, a feature that wasn't previously available.
The mod will also offer "updated effects, textures, models & maps," a 3D interface designed specifically for VR, "realistic weapon interactions," and "multiple VR locomotion methods," which I assume means ways of moving around in the game world. It'll be free too, but will require ownership of Half-Life 2, and HL2: Episode 1 and 2, in order to run. If you like what you see—and it's Half-Life 2 in virtual reality, so by all rights that should be a big ol' "Yes please, and thank you."