The game itself is good. No ads (unless you choose to use ads for stuff), decent graphics and a well built system. It is all ruined though by the core aspect of the game which is the towers which can be infinitely be upgraded and merged for no price. No costs required to upgrade, no costs to build. The only things you can alter about them is their range and damage which means you can almost instantly overpower your defence meaning their is no difficulty in defending against the zombies.