John Bedford (Modojo): In the unlikely chance that you've never encountered a tower defense game on your mobile phone before, they work a bit like this. First of all, you get a map with some starting cash. On the map, you need to buy and place various types of defensive towers using the cash you have, and watch them assault the invading waves of enemies. Rinse, repeat and expand with extra cash you receive for defeating the invaders. It's much the same in Bloons TD 5 but there are plenty of twists to keep this very familiar genre feeling fresh.