Google Nexus one is not just a phone. It can also be used as a game console since android 4.0 adds such additional software and hardware support that the phone can act as a game console
One can connect it to an external display with HDMI out and can also connect an external game pad to play games and take the display out there in external display. Thus turning the phone into a full featured gaming console.
Although there are not many supporting full featured hardware accelerated games out for the new and powerful devices like Google Nexus one, but with the release of the SDK, we can certainly hope to find many new games coming up or games from other platform getting ported to android 4.0.