Ok am i alone in thinking this??? semi-spoiler
I've been digging around, it seems like the Ursula le Guin novel doesnt really have this interpretation, but after watching the movie for a second time, I can't help but feel that George, and everyone in the world is dead. He is alone in his own heaven, and everything is an extension of himself.
This would explain the title perfectly, being the person who dictates your own heaven. George was confused and his thoughts were muddled thats why Portland was such a hell-hole. The Aliens may or may not be seen as God telling him: the ability to accept what you know and not try to dig too deep is a gift. Haber represents the side of George that is power hungry and wants answers, and Heather is the side of him that is just telling him to be happy and live with what he wants, which he eventually does... I mean, the world ended, that's why he says to Haber: you saw what happened after April, didnt you? The only descrepency being: aunt Ethel, that just wouldn't fit the theory.