The points on which this one differs from the musical remake, is what makes this one a genuine horror movie.
Where the musical version tries to make sense out of people's motives, this one does not really go into why Seymour is so remorseless for the most part of the movie. Neither does he need a real motive, unlike the remake that has a charismatic plant making promises. I found the plant in this version to be surprisingly unable to fend for itself. As I'm not really a horror fan, I do prefer the musical version myself, but I quite understand why it's appreciated by horror movie adepts.