I have some fond memories of this episode. It was the first one I ever taped, and it sort of marked the beginning of my Friends fandom.
Chandler and Janice have their only "real" break-up in this episode. Earlier in this season Chandler has actually been in love with Janice, only to find out she's cheated on him. Now there's irony; the only time he's committed to their relationship she's not. I was actually sort of sad to see Janice go; she is a great person and she does seem to care for Chandler. Cheating aside.
Anyways, I loved Joey's role in it. He's definitely not a fan of Janice, but he doesn't gloat in what's happened and he's not happy that they'll be rid of her. He's sad because Chandler is hurting. And he shows his mature side which we get to see so little of in the later seasons. Joey was great in this episode, and Matt LeBlanc's performance was one of his best.
Chandler's talks with Janice were also really good. Both when he called her on her affair and when he broke up with her. Classic Chandler.
Meanwhile Phoebe believes that whenever she goes to the dentist somebody dies. It was quite the odd storyline, but it worked for Phoebe. It provided a lot of comedy and showed us how much Phoebe cares about the people around her.
Ross has an emergency at work and leaves Monica in charge of Ben, though let's Rachel believe that she has the main responsibility. It ends up being Monica who screws up by accidentally bumping Ben's head against a beam in the apartment. As the case mostly is on sit-coms they come up with very strange ways to cover it up. Their plan doesn't work however as Ben keeps saying "Monica bang". I remember how fans of the show said "it sounds like he's saying Monica Bing" when this episode was new. Perhaps Ben has some of the psychic powers Phoebe believes in? ;)
One more thing that made me like this episode was that they all had their different storylines, but towards the end five of them joined forces to poke Ugly Naked Guy with a stick (a sentence you don't write every day). I always love when they do things together as a group.