Seeing some people here dismiss Half Life....
Each HL game revolutionised or evolved gaming in some way at each of their respective releases. A HL3 would break the internet not because of it's name and legacy but because of what it will bring to this sterile industry that has done nothing interesting in a decade.
Advancements to AI,physics,destruction,design...you know....all these very important things that have been completely neglected by developers for over a decade in pursuit of 4k,Ray tracing and image reconstruction techniques....Because making the specks of grass look less jagied in an utterly boring ass game is revolutionary in today's industry.... That or getting pronouns in your game like it's some huge breakthrough.
HL3 If its ever announced will be a game that thoroughly advances the medium as its predecesors did.
But for what is worth...I don't think it will be announced otherwise Geoff would be screaming from the top of his lungs how "hype" his shitshow will be.