Duplex is a comedy that could have been a very funny movie. As it is, it is a reliable second rental on movie night.
Anyone who has been a tenant will relate better to the premise of Duplex and its stars, Drew Barrymore and Ben Stiller, than a homeowner. The setup is a young couple buys a house in New York. Because they are a bit greedy, thinking that as soon as the rent-controlled little old lady dies (she does seem to be in bad shape) the house will immediately gain in value, they are punished.
Without revealing the punchline of Duplex, let's say the little old lady ain't so sick and helpless. Both the Drew Barrymore (a very funny comedic actress) character and the Ben Stiller (could have been anybody else and the movie might have been funnier) character go nuts trying to live with and accommodate their aging tenant.
Duplex is a movie with a lot of cartoonish simulated violence of the slapstick genre. Ben Stiller is decent in his role but Drew Barrymore steals the show. I think Duplex could have been a very funny movie if someone else had taken the role given to Ben Stiller.
Stiller is not that interesting an actor and not that funny no matter how funny the character could have been. He constantly gets upstaged by Harvey Fierstein (no sin, Harvey Fierstein is a huge presence in any movie he is in) but also by second banana Robert Wisdom who plays the cop the young couple constantly has to deal with when something happens to the old lady.
Unlike many recent comedy movies, Duplex is tight. There are no extra long scenes and no unnecessary scenes. It is a very good and reliable second pick if you are going to have a movie night with a comedy.