The difference between Robin Williams and Micheal Jackson is that when Robin plays and hangs out with young children, you believe he really is in it just for the fun.
If you are trying to test to see if someone is a vampire, demon, or other soulless creature just have them sit through this movie and watch for a damning absence of tears.
Coppola and Williams' attempt at recapturing the glory of Penny Marshall's Awakenings, except there's no De Niro, no memoir as source material, and we are told the lighter side of Werner Syndrome ala Mad Magazine.