I had the opposite problem. My DD (now 6) HATED characters until this year. She screamed bloody murder every time one came near her and I have the pictures to prove it! She still doesn't like all characters, in particular Capt. Hook scares the beejeebers out of her.
Just something to think about. If your DS hasn't met any giant furry characters yet, he might not like them. When I got to thinking about it, it's actually pretty smart (and instinctive) for a little kid to avoid anything large and furry that could potentially EAT him or her...