This time towers are locked from the start and you have to progress through the levels, place towers and gain cash. Also once you have upgraded towers enough you will need to beat the game to upgrade them further.
Bloons TD is back and better than ever! With much more explosions, towers, graphics, tracks and bloon types. There really isn't anything that isn't new in this game and with modes like sandbox, apopalypse and normal modes the game will have you playing it over and over again until you can't play it anymore. And then you will play it more.