I did a search on "bloons" before I posted anything, so maybe this is new to some. It is addictive! At least it was for me for a couple of months
http://www.ninjakiwi.com/Games/Tower-Defense/Play/Bloons-Tower-Defense-4.html The track I play is "Tap Hard"
Getting to level to 75 is "easy" , after that it is a real challenge from 85 onwards. I think I officially got to 120 'ish, but (from memory) I got to about 135 when my computer crashed (then I got pissed off and gave up)
Let me know what you think.... BTW there are easier versions: Bloons 1,2 and 3 :!:
I knew there were cheats hacking the system when I was playing, but it seems I was #1 in this game 135 days ago (after some reset) and I never realised. My best score is registered as being 78... that's easy for me to beat :!: Maybe you will see me again on Tap Track Hard :bball: