The movie has a long lineage--the original story came from a 1960 non-musical Roger Corman film (featuring a very young Jack Nicholson), which was then developed into an off-Broadway musical in 1982 that later became the 1986 movie. The basic storyline stayed the same throughout: a nerdy florist finds fame, fortune, and romance by nurturing a carnivorous plant that soon becomes too monstrous for him to handle.
The original Corman film was famously shot in only two days, but the musical version has much higher production values. It was directed by Frank Oz, whose vast experience as a Muppeteer led to the elaborate creation of Audrey II (the man-eating plant), which seems like a truly living creature throughout the film. Puppets for the plant were made in six stages of its growth, and the final one required 60 technicians to operate it!
Oz also filmed an intricate Godzilla-style ending to the film, which never made it to screen. The plant wins in that version, and although that ending holds true to the original movie and stage musical, test audiences found it too depressing. The original ending can still be seen and it's truly impressive, but I'm afraid I have to agree with those original test audiences. I mean, who wants to see lovely Audrey devoured by the plant?
The whole soundtrack is worth checking out for the songs themselves, as well as the talented singers who sing them. Since the movie takes place in the early 60s, the songs were written in the style of early doo-wop, Motown, and rock and roll, and a genuine Motown R&B star is the voice of Audrey II--Levi Stubbs, lead singer for the Four Tops. Here he is (or his voice, anyway) in the climactic scene where the plant reveals its true origin and intentions to Seymour.
Look out, here comes Audrey II!