I'm a sucker for anything stylized. I loved Jet Set Radio Future because of the art style. I love Ninja Gaiden 1&2 (THERE IS NO NG3. *plugs ears and closes eyes* LALALALA) because of the fluid and acrobatic combat.
Of course, substance beyond style has to be there, or it'll get boring quickly.
EDIT: Actually, this thread should be in the "General Discussion" section.