Eww to all you people who are talking about large budget symphonic scores when talking about video game music (Even if I'm being a bit hypocritical here).
The game source in my links is not really a large budge title. It is very basic compared to most games. Heck Civ 5 looks like Crisis compared to CK2. The music provides an atmosphere the graphics can not. Music scores are a major part of the developer's practice given the genre is strategy simulation on a world scale. Not to be confused with an RTS which is limited to a "zone map"