Halo

The Halo series is often type-casted as just another videogame series, but I believe videogames can be just as good or bad as any other forms of art. Halo games have great gameplay, graphics, and most importantly, great soundtracks. Martin O' Donnel wrote the scores to the first three Halo games, and all of these selections are by him. He's a fantastic composer, and I believe he should be doing movies. 

1) The Halo Theme is probably the most iconic videogame theme besides Zelda or Mario. A gregorian chant-like piece is not what one would expect from a shooter, but this piece works so well with this game. It's a haunting work that really picks up throughout and becomes a great action piece. It really sets the mood for the sci-fi nature of the first game. 
Halo Theme


2) Unforgotten is featured in Halo 2. Here, O'Donnel delivers a surprisingly emotional piece full of both sadness and strength. It's a stirring work that seems to come out of a movie rather than a videogame. 
Unforgotten


3) The Epilogue piece to Halo 2 is similar in its emotion to Unforgotten, but it has a greater sense of closure. The strings paint a beautiful backdrop to the ending of this game. It's an amazing work. The guitar solo in this piece is amazing as well- I would die for that tone. 
Epilogue