Thanks for the edit to the original comment; I was unsure whether you were arguing for a view or just describing it (though I assumed the latter based on your other comments).
Without God there's no end game, just fleeting existence.
Like the statement in the original comment (and like most arguments for religion), this one is in great need of unpacking. People invoke things like "ultimate purpose" without saying what they mean. But I think a lot of people who agreed with the above would say that life is worthless if it simply ends when the body dies. To which I say:
If a life that begins and eventually ends has no "meaning" or "purpose" (whatever those words mean), then an infinitely long one doesn't either. Zero times infinity is still zero.
(Of course I know what the everyday meanings of "meaning" and "purpose" are, but those obviously aren't the meanings religionists use them with.)
Edit: nerzhin points out that Zero times infinity is not well defined. (Cold comfort, I think, to the admittedly imaginary theist making the "finite life is worthless" argument.)
I am a math amateur; I understand limit notation and "f(x)" notation, but I failed to follow the reasoning at the MathWorld link. Does nerzhin or anyone else know someplace that spells it out more? (Right now I'm studying the Wikipedia "Limit of a function" page.)
Sometime ago Jonii wrote:
When I'm hungry I eat, but then I don't go on eating some more just to maximize a function. Eating isn't something I want a lot of. Likewise I don't want a ton of survival, just a bounded amount every day. Let's define a goal as big if you don't get full: every increment of effort/achievement is valuable, like paperclips to Clippy. Now do we have any big goals? Which ones?
Save the world. A great goal if you see a possible angle of attack, which I don't. The SIAI folks are more optimistic, but if they see a chink in the wall, they're yet to reveal it.
Help those who suffer. Morally upright but tricky to execute: James Shikwati, Dambisa Moyo and Kevin Myers show that even something as clear-cut as aid to Africa can be viewed as immoral. Still a good goal for anyone, though.
Procreate. This sounds fun! Fortunately, the same source that gave us this goal also gave us the means to achieve it, and intelligence is not among them. :-) And honestly, what sense in making 20 kids just to play the good-soldier routine for your genes? There's no unique "you gene" anyway, in several generations your descendants will be like everyone else's. Yeah, kids are fun, I'd like two or three.
Follow your muse. Music, comedy, videogame design, whatever. No limit to achievement! A lot of this is about signaling: would you still bother if all your successes were attributed to someone else's genetic talent? But even apart from the signaling angle, there's still the worrying feeling that entertainment is ultimately useless, like humanity-scale wireheading, not an actual goal for us to reach.
Accumulate power, money or experiences. What for? I never understood that.
Advance science. As Erik Naggum put it:
Don't know, but I'm pretty content with my life lately. Should I have a big goal at all? How about you?