I never knew there was another version of Little Shop of Horrors. I got it based on the clue, but didn't remember him in the movie. Also, this quiz made me realize how few of Jack Nicholson's films I actually like. In particular, Easy Rider and The Shining are considered classics but I am not a fan.
A Few Good Men is amazing, and Batman is pretty good. The rest of this list is movies I haven't seen or movies that didn't leave a particularly strong impression.
Chinatown, The Departed, and One Flew Over the Cuckoo's Nest are some of the greatest films of all time. The Shining is my personal favorite of his and is tied with One Flew Over the Cuckoo's Nest for his best acting performance. Like you said, A Few Good Men is amazing and Batman is personally one of my favorite DC movies and he plays one of the best Jokers, although nowhere near Heath Ledger. As Good as it Gets is really good and The Bucket List is a good movie as well.