Despite all the jokes, it's not a happy story most of the time. Actually the one thing that's constant on Friends is that they're failing. I can't count how many times they lost their jobs, how often they had to work crappy jobs they hated, how often their hearts were broken, how often they failed at achieving the thing they wanted. This reaches from little everyday goals to major life goals like having a child. That's the first thing I love about Friends: It somehow makes it okay to fail. If even your tv heroes don't have their lives together, than maybe we ordinary real life people are not such loosers after all.
The other thing is that regardless of all the disappointments and setback the Friends characters have to permanently face, it's still a show which makes you happy. Because through all this crap they never loose their humour. They make jokes about everything (even about things which would be extremely inappropriate to joke about in the real 21st century world) and they laugh a lot. They aknowledge that life sucks but they laugh anyway. Because really, what else is there to do? Maybe the only way to deal with all this ugliness is to joke about it. Preferably with your best friends.
For me in the end it's all about this: Life may suck but as long as they have each other it's all going to be okay. And isn't this true even outside of sitcoms? You may not be where you wanted to be, in fact you may be so far from that place that you doubt you'll ever get there, but as long as you're surrounded by the people you love and who make you happy, you're doing fine. You're doing great.
The Friends theme song says it all: