One of the first things I noticed on this watching was how Danny Elfman-like the theme music was. Lo and behold, Elfman was the composer for the film. Of course, this makes sense given that the movie was directed by Tim Burton and Elfman is his composer of choice.1
Finally, this movie wouldn't be the classic that it is without the ghost with the most. Keaton delivers a fantastic performance as the titular bio-exorcist. His character is slimy and disgusting and makes you feel dirty just watching him. Despite this fact, you can't help but enjoy all the scenes he's in. Even if you haven't seen this movie for years, I recommend watching it again for Keaton's performance.
1. Of course, Michael Keaton and Winona Ryder later starred in Burton's Batman and Edward Scissorhands, respectively.