[nitrogen]

Duke Nukem Forever is one example of this.

But Black Mesa is a counterexample; they still haven't released Xen last time I checked, but everything they have released far exceeds expectations. Maybe Valve should pay that group to finish the HL series.

[arianon]

The first three maps of Black Mesa: Xen were just released a few weeks ago, actually.

https://www.youtube.com/watch?v=IzR3vllw6O0