It's interesting, because you consider an atheist's existence to be "sad" (my words) because we don't have some wondrous afterlife to look forward to, but I consider your existence to be sad, because you cannot enjoy your current life without said promise of eternity.
What cyclic disdain we have wrought.
I beleive you misunderstand my thoughts a little. And I think your summary is off.
I can enjoy this current life as much as anybody else, and I beleive even more than others.
Imagine for a moment that you knew with 100% certainty that there was a God. This God created you in his image, to worship Him, to give glory to Him.
Ok, you are still imagining that you know for a fact there is a God.
You know, through his Word, that glorifying him through Biblical prinicples brings him honor and glory. That obeying give Him great pleasure. What an awesome thing to be able to do while here on Earth! To make the God of the universe who has created you, and given you life, well pleased. To have Him look down on you with favor. What a wonderful thing to be able to give to Him right now.
Ok, you can stop imagining now !
The wonderful part about pleasing God, is that you can do it no matter what your circumstances, whether in sunny days or the bad ones. The 'afterlife' is not on our minds all the time like I think some people beleive. No, we are very much focused on today.
I totally beleive that many atheists live happy lives, but when you decide (if you decide) to start thinking about the further off questions about life, and what is next, who wouldn't be depressed to not have an answer ?