Its the voice acting and surprisingly crisp animation which makes the Sonny series as popular as it is. Also the simple and interactive gameplay and well composed music make it popular. TRUdog its the small details which allow a game to actually become popular.
Do we really have to know why? I mean as long as we like it we don't ask questions. And if you don't like it, screw you. lol, Just kidding, but I was serious about the first part.