Operation: Black Mesa is a total Source remake of Half Life: Opposing Force. Using the Source engine, the developers plan to recreate the Black Mesa research Facility as it was seen by Corporal Adrian Shephard of the H.E.C.U. Half-life: Opposing Force is still an amazing game, although it's not nearly as amazing as it was when it was released.
This picture captures part of "Missing in action" recreated by FRAG. Work in progress!