Bloons Tower Defense 2 introduces 3 levels of difficulty and will prove quite a challenge compared to the 1st game. It does however feel more like an upgrade or patch on the first game...

I would advise you to take a look at the 3rd Tower Defense game which is far superior and offers one of the best defense games in the free online games category. Bloons Tower Defense 3 will prove one of the best Bloons games you've ever played!