A singleplayer mod for Half-Life based on a new version of Half-Life FX engine. While the main mod, HLFX:Single, that uses maximum of engine features, is still being developed, you can have an opinion of relatively small project entitled HLFX: Lost in Black Mesa.
I liked the attention to detail, and the great HD models and effects... but that's about it :(
Simply put, the level design was rather dull. It was just a maze of railways without any differing features per level and a brief exterior level.
Other then that, give this a try if you want to see how far Goldsource can be pushed. :)