but isn't the entire world and the universe dark, cold, and depressing?
Not really. I think the world, at least the part of it where I live, is a great place. I can't remember the last time I was depressed, really.
And now, let's assume there actually was a God. Why would we worship him?
The fact that he has done nothing to prove his existence could mean one of the following:
a) He does no longer pay attention to this world. Maybe he went of to create another world on some distant planet, or maybe he got a new hobby.
b) He does not care about individuals. Maybe he's still around, keeping the world spinning, keeping them asteroids from blowing us up, and making sure global warming doesn't turn us all into ashes, but that doesn't mean he has an active part of every person's life, nor that he cares about what they do or think of him.
c) He created the world simply to watch it go. Like an ant farm or something. You put the ants there, give 'em what you need, and you let them go on with their lives. You don't magically heal an ant because he has indigestion, and you don't want the ants to pray and shout your name once a week.
Basically, what I'm saying is that, even though I don't believe there is a God, even if there actually was, I'd see no point in worshiping him.
If so many things in the Bible which have been disproved were supposed to be metaphors and taken figuratively, how do we know heaven and hell wasn't too?
In fact, how do we know God wasn't a metaphor too? Someone who watches you, takes care of you, and someone you should trust and do anything for. Sounds like God could be a metaphor for the government or something. Perhaps Christianity was just invented as a way to control the masses?