Lot of favorite shows and interesting points above; too many for me to get into fully when I should be working. But two quick points:
(1) Although the shows were different in ways outlined above and maybe some others, Friends was most definitely an attempt to follow and tweak Seinfeld's formula. There were many others that tried it at the time -- Ellen (originally "These Friends of Mine") being another. They all had minor differences and targeted different demos with their casting and location and story lines etc. But the success of Seinfeld made them possible, as well as more modern broadcast fare like How I Met Your Mother. You could look at that as a Friends reboot, and Friends surely as a Seinfeld derivative.
The derivatives suffer by comparison. In Seinfeld you know that the characters are neurotic, self-obsessed schemers and it never tries to convince you otherwise. Something about that is honest; no "very special episodes" or treacly, cheap inspiration here. As dino27 said to some extent "we are all like that" and so you can laugh at yourself without creating for yourself a false self-image (today we might call that self-image a social media profile). And somehow you find yourself rooting for them anyway (usually -- often not George). The show is consistent in the amount of belief and judgment it asks you to suspend. That is where Friends and some similar shows lost me. At times the characters are also neurotic, self-obsessed schemers, but at others the show expects you to feel genuine affection and empathy for them. In the latter times you are supposed to forget the former, and it only works if you can gloss over your own shortcomings in your mind. That is dishonest. Don't try to make me like Chandler (or whomever), I remember what he did last week. I'm supposed to suspend disbelief and judgment when the characters are acting like privileged, precious little turds and then I'm supposed to use judgment and belief to care whether Ross and Rachel deserve happiness together. The hell with that.
(Btw a modern dark comedy that strikes me much the way Seinfeld did stars one of the same actors -- Veep.)
(2) The first post in this thread from italyprof listed favorite movies with religious themes. I would add to it The Truman Show. I'll have to leave it at that for now since I spent too much time rambling already. Felt a bit like "Get off my lawn!"