Welcome to the forum. We actually have a thread about Showtime already. Showtime is pretty different from LN. Showtime is more Vegas-like, and entertainment, while Bridgeport is more LA/New York, night around the down, clubbing and bars.
Both have in common with the Sims 2 Nightlife, with the downtown themes, but Showtime, is more entertainment. Late Night is about bar and clubbing.