IGN has an interview posted (in article form) with Jesper Kyd, who served as composer for the Darksiders II and Borderlands 2 soundtracks amongst others. The article also includes input from Cris Velasco and Sascha Dikiciyan who also worked on the Borderlands 2 soundtrack. Here’s a brief part of what Mr. Kyd had to say:
“I don’t think there is one specific way to score a game. It really depends on a lot of things. For example, during what stage of the development process the music production starts. If the game is still in early alpha I tend to use the concept art that the team is using as well. That’s how I composed some of the Darksiders 2 music. For Assassin’s Creed, there was a lot of focus towards creating a unique signature sound. On Borderlands 2 the game was far along in development so I used concept art, screenshots and gameplay videos for the writing process.” – Jesper Kyd