When APB made it's debut at E3, I was amazed. While others were enthralled by the Natal project or some of the other big names I became obsessed with APB. I read all the coverage, news stories, reviews and in doing so discovered that a lot of people thought this game was groundbreaking but no one had started up a community around it.
The ideas presented, the customization control, the idea of the dynamic generation of PvP matchups makes this game groundbreaking.