She was ok in the first few seasons and played her 'kooky' role well up to about season 5 and had some very funny moments and lines, especially when she gave birth to her brothers babies. After that though her character started to change and by the end she was horribly unlikable and sex obsessed, which is completely different to how she started out.
Joey as well became shitter. He started out a bit dim but he became unrealistically dumb by the last series, not being able to tell left from right.
Actually my favourite episode is the one where Phoebe and Chandler are trying to fake each other out over his relationship with Monica:
"The One Where They All Find Out"
Cut to the bathroom.]
Monica: You go back out there and you seduce her till she cracks!
Chandler: Okay, give me a second! (Pause) Did you clean up in here?
Monica: Of course.
[Cut back to the living room. Chandler slowly exits the bathroom and gets pushed from behind by Monica and sees Phoebe closing the apartment door.)
Chandler: Oh, you're-you're going?
Phoebe: Umm, not without you, lover. (She slowly walks over to him and is showcasing her bra.) So, this is my bra.
Chandler: (swallowing hard) It's very, very nice. Well, come here. I'm very were gonna be having all the sex.
Phoebe: You should be. I'm very bendy. (Pause) I'm gonna kiss you now.
Chandler: Not if I kiss you first.
(They move closer to together and Phoebe hesitantly puts her hand on Chandler's hip. He puts his hand on her left hip but then decides to put his hand on her left hip. Phoebe then grabs his butt. Chandler goes for her breast, but stops and puts his hand on her shoulder.)
Phoebe: Ooh.
Chandler: Well, I guess there's nothing left for us to do but-but kiss.
Phoebe: Here it comes. Our first kiss.
(They slowly and hesitantly move their lips together and kiss gently. Phoebe has her eyes wide open in shock and Chandler is squinting. He finally breaks the kiss after only a short while and pushes Phoebe away.)
Chandler: Okay! Okay! Okay! You win! You win!! I can't have sex with ya!
Phoebe: And why not?!
Chandler: Because I'm in love with Monica!!
You kinda forget what a huge social phenomenon this was. It was probably one of the last TV shows where everyone watched the episodes at the same time and talked about it the next day.