Has it really been 20 years? Blimey! Black Mesa, the fan-made recreation of the original with plenty of bells and whistles has a trailer for the hotly anticipated Xen levels.
Feast your eyes:
As for when we might finally see the Xen levels ourselves? The Black Mesa team say they're aiming for Q2 2019 so we still have quite a while to wait on it. Good things come to those who wait though, no one wants to see it rushed.
They say they're happy with the design and they want to ensure it's fun. Most of it is "design locked and functioning as intended" so the remaining time is to just finish it all up. They're estimating the Xen levels will take around 6 hours, more if you're a keen explorer.
It's also interesting to see how they made more of a splash about Half-Life being 20 years old than Valve themselves did, which was, well—nothing.
See more on Steam.