The first game in the series, Bloons Tower Defense was basic, with only the Ice Tower, Dart Monkey, Boomerang Thrower, Bomb Tower and Super Monkey. However, it received very positive ratings for its tendency to be fun and addicting.
Bloons Tower Defense 3 added even more towers and updated the Bomb Tower's sprite.
Bloons Tower Defense 5 added even more Towers, and introduced NinjaKiwi's login system and the Awesome Points, a new system as-of-then recently introduced to the website. It also introduced a massive graphics update.