Two wildly different shows come to mind.

"Celebration!" - a musical by the men who wrote "The Fantasticks".  It's an allegory that takes place on New Years Eve where a young man, an "orphan in the storm", comes across a party being given by an amazingly rich old man who can buy anything he wants, except the youth he has already lost. There are four leads: a Narrator, the Young Man, the Young Girl (a singer at the party), and the Old Man.  The rest are revelers who act as a Greek chorus as the battle between rich and poor, young and old, plays itself out.

"Die Fledermaus" - the great Strauss operetta.  Get a good English translation (there are several).  It also takes place at a New Years Eve party.  Mistaken identities, possibly unfaithful partners, an elaborate practical joke, a maid on her night off, and a police inspector on a bender - all at a party hosted by a a handsome prince.  The score is spectacular; and it's an annual  New Years event at many theatres around the world.  Six major roles, plus one great non-singing comic role, and the biggest party ever seen on stage.  Tradition also allows for a variety show to be inserted as entertainment at the party; often utilizing contemporary specialty songs to great comic effect.