As far as tower defence games go, this is quite simple and for the first two levels, quite enjoyable. Level three is however is far too difficult for so early in the game and it sucks all of the fun out of playing the game. I can imagine a fair few players will never see past level three. If you do persevere, that level requires a very rigid placement of towers, otherwise you are doomed fail, over and over. Ican't give the game more than three stars as I think they've made a big mistake, by not including a difficulty setting.