The multiplayer component is THE deal breaker for me. Valve just wipes the floor with the competition - that's why they're so successful. They know what gamers want (community, multiplayer, non intrusive DRM) and are fully open to the modding community. This is why PC gaming will always live, because even if the last developer on Earth stopped doing games for the PC, there's always the modding community providing more content for gamers to keep on playing the games they have.