Casper's been using steroids! I like the laid-back mood of this picture, the relaxed poses and rather casual, leisurely tickling approach of the specter. Well, relaxed for the ghost, at least... he's getting a pretty big reaction from his vicitm!
The ghost reminds me a bit of the one from the Ghostbusters' logo. So +1 points for that. I like the way you drew the victims, too. Something about the eyebrows, though. She almost looks a little mad. Overall it's really cool, though. n_n