Okay. This game is great, but it needs to go somewhere. Just four options (easy, medium, hard, abyss) are not good enough. Look at Warlords: Call to Arms, or Gemcraft. They had a nice engine, like you have, but they took it somewhere, on an adventure across the land you know? They used an overworld, and had skillpoints you could upgrade over time. This increased the replayability of those games tenfold. Another thing, from one developer to another, change the size of that damn mofunzone link and reupload the fixed version to Kongregate, it's handicapping the minimap and is just a really newbie thing to see in your portfolio. Other than that, nice game. Not sure if you made them, but I really enjoy the animations.
The game is unbalanced and the addition of "Buying" extra upgrades turned me off right away. Come on guys, don't sell out for the production of crap games. I no longer want another bloons sequel if this is the direction you're taking it. Quit at 4.
Now, I assumed the point would be to kill all the cars on the road. Apparently, they take points away from the whole reason this is game is any fun at all. FFS people want to smash everything, don't punish them for doing so.
 "Idle Sky II"){kind=icon}
 "Learn to Fly"){kind=icon}
 "Miragine War!"){kind=icon}
 "Flash Element TD 2"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "The Heist"){kind=icon}
Done, in the latest update.