On launch, this had an unplayably slow XP grind, suffocating meta, and far less content than btdb1. It's improved somewhat since then, making a playable experience, but I haven't bothered with the game. Much of the changes (besides those to XP and balance to enable basic playability) have been to add more limited-time cosmetics. Some features and modes have been added but I've not bothered to go back and check them out. Also this game drains your phone's battery like crazy. Maybe not the worst game I've played, but definitely the most disappointing.
I'd give it a higher rating because I actually think the gameplay is more fun than Bloons 6, but this game is so horribly optimized and forces you to either grind for hours or spend money to unlock the monkeys and upgrades that will actually let you win games. When you go up against someone who can upgrade their monkeys fully, it's pretty unfair.