I reviewed Half-Life remake Black Mesa—which began development in 2004—six years ago. It was great, but it was also missing something: the game’s final act, set on the alien world of Xen. That’ll be out next year, and if you’re wondering why it’s taken so long, it’s because the section has been almost completely remade.
https://lastchance.cc/black-mesa-the-kotaku-review-5944812%3C/a%3E%3C/p%3E
The Black Mesa team say Xen will be around Q2 2019.