There are four tracks to choose from initially, but you can unlock the other four by beating the first four on easy mode. New upgrades include extra long range and razor darts for the standard monkey towers.
I've just completed the first level and am excited to continue play. The best part about Bloons Tower Defense 3 is that it is much longer and provides more challenges than the previous two. I'm looking forward to see what the so-called secret weapon is.
Play Bloons Tower Defense 3 @ NinjaKiwi.com