The challenges are stupid because the bots do not take instructions well. I would also like to see a no weight limit fun mode as a reward for completing career mode.
The music is very annoying, the jumping distance is a little off, and it is so small I had to put on my glasses - though the last of these is not really a negative mark, just commentary.
The first bloons TD was mediocre and needed a lot of work. This one, well, it is just atrocious. Let's not fix the cost to worth problems from the first one then further compound them by raising the prices from prohibitively expensive to idiotic. I do not even think badges are given by the difficulty anymore, I think they are determined by how probable it is you will get it.
My guns are just shy of tivaelydoc's at 113 and after nearly half an hour I could not kill the boss. I would suggest upping that hard badge to impossible or softening that boss' HP.