Humans must be the most emotionally complex fools ever to have existed - not just on this Earth, but anywhere, anytime. We have the ability to feel deliriously happy, and we have the ability to be depressed to the point of suicide. I refer not just to humans as a race, but to each of us as individuals. Nobody can honestly say that they've never been incredibly happy at least once, and nobody can say they haven't wondered what life is all for. You live, you do things, you die in the end no matter what.
Reincarnation is the cruelest joke. To finally escape from the world and all it's pain, only to be sent back. How hilariously depressing.
As for an afterlife, in heaven or hell or whatever you happen to believe in... it seems to involve harps and joy and God's right hand, but no sex or revenge or endless bookshelves full of good quality science fiction.