I'd have killed for something like the Source Filmmaker when I was younger, and it's fantastic to see so many great videos come out. The amount of time and effort that goes into something like this has to be admired, and when the result is as flawless as the example above, you just have to sit back and congratulate the person who made it.
With voice and sound taken from the movie, The Matrix Remaked is a source-built look at a Matrix world populated by Medics and characters from Left 4 Dead. The majority of the visual work syncs up perfectly with the stuff from the movie and the only time you're really reminded that you're watching a source film (outside of the characters used, of course), is when you notice a familiar location in one of the longer shots.
Definitely worth a watch!