I think it's got a winning formula, whether or not it was intentional or an accident I don't know, but it does so many things right. It caters to casual players (I can pick it up, guess, draw and put it down) or hardcore players (draw + guess all day and all night), it forces people to provide value back to the player they're against (after guessing you have to draw to play another game) and it has a good micro transaction system.

I've never played mobile games properly before but I find myself drawn into playing Draw Something along with all my friends, who like yours love it.