Considering this is season 1, this is very good. The name mixing up is fantatsic, especially when Monica and Rachel are dating the two docters, and they get angry with each other, and take everything a tad too far. It's also very funny when Chandler, Monica, Rachel and Ross all meet in the hospital, because Monica wants to change the forms and Marcel swallowed a 'K'. Their faces when they see each other is very funny. The Joey and Phoebe storyline is great. It shows the begginning of their wonderful relationship in the seasons to come.
Overall, an extremely good episode.