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.
Amazing mod! Seeing these kind of graphics and physics in Goldsrc is very impressive. The only problem is that the Half-Life update ruined it and it will only run in windowed mode.