Sounds closer to Phantasy Star Online than anything else...That was a fantastic gaming experience on the Dreamcast so I can see the appeal...Guild Wars with groups of 4 worked well too...
Playing: Borderlands(great co-op,HUGE amount of content),Too Human(better late than never lol),Saints Row 3(Penetrator ftw),Minecraft 360,Harry Potter Lego.
Patiently waiting for: Tomb Raider, Borderlands 2