The whole human race is an experiment in which we are trapped on a doomed planet, and generation after generation we must try to adapt and create so as to be able to escape or survive the eventual apocalypse, and have our next generations after generations live their lives normally.
Which effectively is meaningless in every case, since not every individual can help here at all, and then you begin to think about how much the lives were really different before and after the 'apocalypse scenario'.
These thoughts also occur in the same conversation which tends to occur after any group watching some sort of Zombie movie. "I'd just die, there isn't anything left man! Wait, unless I was with a girl. Or just a really cool guy, right? No worries, we can do whatever" - what point makes life 'worth living' once people are gone. Is it just people? Family? Sex?
If you take those things away in this world (non-zombie), is it still there for a reason?
I like cats. Sometimes, I watch cats. They are really amazing things, almost indifferent at times, and you never know what is going through their heads. They just live, instinctually. I personally doubt that most cats would ever feel the concepts of having had a bad life or a good life. A cat probably knows that it is being treated well, or badly, and it would like to be treated well more, and badly less. But at the end of the day, a cat wouldn't think "well, this day could have gone better", or "I wish I was that fat white cat on that balcony, eating... is that a whole chicken!!??"
Humans are pretty much the opposite. Which really sucks for us to be honest, I always overthink things, and compare my life to others. (This works two ways though, most people ehre can consider themselves fortunate, for having language/literacy skills and access to very first world equipment (internet) - but the trend is to compare ourselves to the other side)
And then, again, you can compare your own life (this is a trend in my idea here) to that of a Cat. They seem fufilled, you don't, despite being aware, and having some sort of concept of the meaning of life.
In the end, it looks like our only answer is to define it for ourselves - or not at all. We could wake up upon death as another tally in the massive chart of the aliens experiment, and knowing it was all a test, would it change any life of ours?