Can anyone explain to me what it actually is? Everything I've read about it is through this sort of know-nothing journalistic filter.

They often focus on the "kill a monster and it stays dead" angle, so that seems like a real aspect of the system, but it's not an advance. Other companies have aimed at this "persistent virtual world-building toolkit" target before, from Second Life to Blue Mars to Metaverse to Metaplace. What distinguishes Improbable from these other ideas?