This episode is great for a couple reasons: it advances the plot (Joey going to Vegas = the Friends go to Vegas = Monica and Chandler almost get married and Rachel and Ross do) and has some very clever dialogue. Phoebe introduces a game that helps the Friends figure out what they really want when making a decision, which later comes in handy when Ross tries to get Phoebe to remember why she is mad at him. The reason ends up being classic quirky Phoebe--Ross called her boring...in a dream.
My favorite part of the whole episode, however, is when Joey and Chandler are in the car and Joey tells Chandler to "clear his mind" and Chandler says, "Ok, it's completely clear, except for a little purple lamp. Is that ok?" Whenever anyone tells me to clear my mind now, I picture purple lamps.