Kotaku just posted:
Valve Reveals Early Gameplay Of Canceled Half-Life 2 Episode 3 And Why It Never Got Finished
In a new two-hour documentary from Valve, current and former members of the company talk openly about the creation of Half-Life 2 as well as finally spilling the beans on what happened to Episode 3, and even showing gameplay of early prototypes of the canceled game.
https://kotaku.com/valve-half-life-2-episode-3-hl3-update-canceled-ice-gun-1851701011