[Shaun]

An easier analysis: the writing went rapidly downhill after season 5 or 6 and the rest just sucked. All the characteristics were amped up to the point of making all of the characters unbearable. Phoebe in the early seasons: a bit aloof, says weird things, is actually fun to watch. Phoebe mid-run-to the end? Shrieking hippie with an unspeakably horrific background who has a song every other episode. Monica is turned from the group support-figure to an overbearing OCD monster. Rachel turns from girl next door to absolute diva. Joey turns from struggling actor with a loveable dumbness to Grade A idiot and sleaze.

Only two that maintain some level of consistent "good character" are Chandler and Ross, but Ross does become a lot more irritating when they realise he can just rest on a one-word catchphrase.