Towers should be identified by name somewhere other than the initial card that unlocks them. Perhaps a reference codex for tower, enemy types that explains things?
Is there a trick to level 22 or does this require really precise timing? I can't, for the life of me, seem to get three shots off before the third balloon growth. Everything up to that point was easy, but...
Considering that you have to beat that campaign to access it, Endless mode is kind of slow. Maybe up the starting enemy frequency/quality significantly so you don't have to play for so long before it gets fun?
It's fun, but there ought to be more things to do with your gold. You end up with a tremendous amount of gold and nothing to spend it on midway through the game.
Its fun, but I've played a lot of games that call themselves "rogue-likes" and this one is probably the least like Rogue (which, come to think of it, is quite an accomplishment in this "genre.")
But deep in the game (I'm on day 295) getting perfect days for the additional 30% income is important for keeping up with the enemy difficulty curve. The problem with trash mobs like rats and dragonflies is that they move fast, and come in great numbers. With Sandbag 10 on day 293 a dragonfly does 7 damage. 3-4 of them can ruin your perfect day, since you might not be able to leech fast enough.
I like how deep in the game (past day 200, say) the least intimidating enemies include things like "dragons" and "tanks" while the most intimidating enemies include things like "dragonflies", "rats", and "crows."
It strikes me as odd that racers will just ram you from behind, rather than attempting to go around you. Even if you're, say, in first place and they could easily pass you but end up in 3rd or later because you both slowed down due to the collision.
Really badly needs a keyboard shortcut for "pause game, and open the upgrades menu". In a game entirely controlled by mouse cursor placement, having to navigate to the upper left corner to pause is pretty suboptimal
"Walled Cave" and "spelunker" aren't awarding properly. Have over 60 walls installed in my cave and have been to level 100 of the unfinished dungeon, and I have neither award.
 "300 miles to Pigsland"){kind=icon}
 "Tesla: War Of Currents"){kind=icon}
 "The Great Bazooki"){kind=icon}
 "Sentry Knight"){kind=icon}
 "Zombinsanity"){kind=icon}
 "Elona Shooter"){kind=icon}
 "Earn to Die 2012: Part 2"){kind=icon}
 "Incursion"){kind=icon}
 "SuperBikes Track Stars"){kind=icon}
 "Bloons Super Monkey 2"){kind=icon}
 "Dungeons of Kong"){kind=icon}
 "Bloons TD 5"){kind=icon}
 "Arkandian Explorer"){kind=icon}
 "Were you a Nineties Gamer?"){kind=icon}
 "Tyrant"){kind=icon}
 "Zilch"){kind=icon}
Done!