I wouldn't call SWINGERS underrated, considering it launched both mens' careers and generally considered terrific 1990s pop culture capsule. (Shit Spielberg casted Vaughn in LOST WORLD after he saw SWINGERS.)

One I would include was DAYBREAKERS with Ethan Hawke and Willem Dafoe, which because it was a slick, entertaining horror movie tanked in theatres. (People want their safe, boring horror movies that just don't try.)

Anyway it had a novel concept: A global population now mostly vampires, what are the implications in society and technological for such a demographic shift? Rather intelligent, yet very watchable slick no plodding genre entertainment that reminds one of John Carpenter.