Indiana Jones is the king of the action/adventure genre. While James Bond is every bit the globetrotter Indy is (and has almost six times the number of movies under his immaculately tailored suit), Bond is a little too neat and debonair to hold the crown. Indy is rough around the edges, and uses his wits more than gadgets to get himself out of, and into, dangerous situations.
The adventure part comes for the sheer spectacle of the film's action sequences. They feel like video games (and have inspired them) and combine action, suspense, and the thrill of discovery.
Indy doesn't just get caught in a trap—it's a trap filled with skulls, spikes, and giant insects. He doesn't flee the bad guy's lair on foot—he does it in a mine cart traveling at breakneck speed.
These movies set the standard for every adventure movie to follow. Nicolas Cage wouldn't hunt for National Treasure and Noah Wyle wouldn't have a post-ER career as the Librarian were the trail not already blazed by Harrison Ford. (Source)
Plus, Temple of Doom has a romantic element. Although, when Indy and Willie embrace at the end, she is less a romance for him than a reward, like the Sankara stones themselves.
Because Temple of Doom is a prequel, we know she'll be replaced by Marion Ravenwood by the time Indy decides to raid the lost ark. Who knows where Willie ended up after the credits? Maybe she married a Hollywood film director…