My partner and I have been watching Friends. She just pointed out that we're about halfway through the series, and I feel that is worthy of comment. Thing #1: Spoilers. I would appreciate it if you did not comment all the details of what happens in all the story arcs after season 5. That said, I will be commenting on things that have happened so far, so if you are also working your way through the box-set, and are further back than I am, you may want to circle back to this one at another time. I believe we're somewhere in early season 6, but I might be mis-remembering.
Thing #2: Ross and Rachel are terrible people. I kinda wish it was a pattern, that everyone in the show whose name started with R was awful, but Richard was a really good person as far as I could tell, so I don't see that theory panning out.
Everyone in this show displays some problematic behavior, but Ross and Rachel are, I think, the only really, really terrible people. Monica's problematic behavior largely stems from her obsession with cleanliness and with being the best at everything, Chandler's behavior mostly stems from his severe low self-esteem and fear of intimacy, Joey's self-absorbed, impulsive and dishonest with the women he sleeps with, and Phoebe's got a lifetime of accumulated superstitions and traumatic experiences that make it virtually impossible for her to make consistently reasonable decisions.
But Ross and Rachel just do awful things. They consistently treat other people (their friends and everyone else) like they're around for their benefit, they both take extreme positions in any argument, which place them as unequivocally right, and they're dishonest with themselves to the point where it compels them to make harmful decisions, even (and especially) when other people point it out to them.
So I really don't care what happens to Ross and Rachel. I just hope they don't screw things up for anyone else.
Thing #3: Chandler and Monica are my favorite characters, and Chandler/Monica is my OTP. Unlike Ross and Rachel, they only generally let their neuroses and insecurities take them to a place of mild wrongness before they allow themselves to be dissuaded. (Except in any case where Monica is trying to win something that has been clearly characterized as a competition.) And they've been growing into better people as the series goes on, unlike Ross and Rachel, who came into the show on a down-note and kept up momentum since.
Thing #4: I don't have anything against Phoebe and Joey, I just haven't been really engaged by their plots lately.