Sign up with GoogleThis story tales place after HL2, a long extensive mod and free (if you dont want to pay for Valve's Episode1) I played this on medium and there were some very intensive fight scenes where I kept losing until I got it right. 
http://www.planetphillip.com/posts/leons-coastline-to-atmosphere-single-player-half-life-2-mod/
http://www.planetphillip.com/posts/leons-coastline-to-atmosphere-single-player-half-life-2-mod/