Probably the definitive, ultimate tower defense game out there and definitely the best one in the Bloons franchise. The amount of content and things you can do are astounding for a simple concept and allows you to play in generally whatever way you feel; there's enough simple maps for the casual side and extreme challenges for people who want to treat is as less of an idle game. There's even plenty of online modes if you're so dedicated to beat whatever challenges the community provides.

That said though, the game does have some drawbacks: some of the most interesting ways to play involve either going out of your way to beat every challenge presented to you regardless of how you want to play or paying up for something simple, and despite it being the ultimate tower defense, that doesn't bring it up from still being just a tower defense game.

It's well worth the time and skill to get into it, as well as being highly affordable, but if you're not a fan of either Bloons or TDs it's hard to recommend. It's an easy and absolute recommend if you are, though.