"THe problem with beautiful productions like South Pacific or Gypsy, is that people who aren't very familiar with theatre, for the most part, won't appreciate the history behind it."
When these shows first came out audience members didn't appreciate the history behind the shows. He can enjoy the show for entertainment purposes. They both still have great music, fun sogns, wonderful acting, and they are full Broadway productions. Though I wouldn't recommend Gypsy simply because it may be too long.
What does your Boyfriend like? That should factor in. I don't think simply because it's his first show should decide which show you guys see.
On that note, if "he likes everything" or "doesn't care," I'd recommend Wicked, Hairspray, Spamalot... These are all Broadway productions with costumes, dancing, singing, everything, adn can give him a true Broadway experience. Hopefully seeing one of these will make him want to come back for more (especially if you are together for a long time. You won't want to drag him, he'll willingly go

)