Here's a trailer for Warhammer 40,000: Space Marine, detailing the class-based multiplayer. As Conrad already told you, there are three classes to choose from, and they can be fully customized with perks, chapter colors, and armor pieces.
According to the video, there are 1.8 billion customization combinations, which is ridiculous.
This game is easily among my most anticipated of the year. Really looking forward to it.