Balance suggestions including a bug fix.
While Kingdom Rush has some stellar balances, there are still nuisances going on in the Steam version that I need to suggest.
*Bug fix: please for the love of God EXPAND THE DAMAGE RADIUS OF THE AREA OF EFFECT ATTACKS. As it is, they're a pathetic joke, such that a Skeleton can be right near the center of a HOWITZER blast and still manage to have full health. Yes, Rain of Fire and cannon blasts need to be condemned to Valardul precise to do any damage. Add to it that the enemies like to enter spread, most notable in instances like Icewind Pass's Wave 12, which is supposed to be built to ask if you have some Big Bertha action going on (although accepting other builds), and things get out of hand fast.
*Have Musketeers' attacks (all of them), Arcane Wizards' basic attack, and Barbarians' melee attacks (but NOT Throwing Axes) all ignore up to 30 points of the targeted DEF stat. All 3 have flow problems at the moment that even extend past the buff idea, deserve to at least be able to hurt armor guys, and have doing that make actual sense anyway. Musketeers can't even handle floods either way so hurting Dark Slayers should be plausible, Arcane Wizards can lose their immediate damage because a demon was in front and shouldn't be penalized so harshly for that happening, and Barbarians should be able to hurt Dark Knights.
*Sorcerer Mage should deal less damage. I would recommend 35~65 base and 8/s Curse, as opposed to the current 42~78 base and 10/s Curse. They would still control armor baddies, they would still be the go-to mage for groups, and they would still do some hurt on Magic DEF enemies, but they would not be able to control the singleton enemies such as Troll Chieftains and Rocket Riders nearly as easily. The Golem also should be given an actual respawn time so that players would want to actually maneuver it.
*Wrath of the Forest should be nerfed. It should ignore only a portion of the DEF rating, not all of it. Levels 2 and 3 also should cost more at 200G each. The reason being that WotF is incredibly synergetic with other towers regardless, whereas Musketeer Garrison's special abilities has a problem with redundancy going on.
*Generally tone up More Axes and tone down Throwing Axes. More Axes is only good with micromanagement to make sure the Barbarians stay alive and keep dealing damage. It seems good because it's crowd control, but the fact is that it can control only 3 baddies at a time and the Barbarians themselves die after extended combat, plus MA can become bad against demons because you can inadvertently kill them and cause the Barbarians to take the explosions. Throwing Axes also requires micromanagement and doesn't seem as good against floods, but it is innately safer, has more potential range than MUSKETEERS with some actual control over who they attack, and can hit flying baddies. I would say decrease MA's first level cost considerably, and increase TA's costs for levels a bit and decrease TA's damage from (24~32) + 10L to (16~24) + 10L.
*And please for the love of God review the Skeletons and ESPECIALLY the Skeleton Knights. As well as the bonus levels and their exclusive enemies. They're generally more dangerous than they should be.
I will say, though, that you did do some welcome things for rebalancing:
*Rain of Fire dealing less damage, period. (This seems bad, but aside from the God forsaken radius nerf of area attacks that proves to be too much, less RoF damage has not proven unmanageable.)
*Musketeers having DEF ignoring at all, though the amount is underwhelming.
*Damage round-up, which even tones up both Arcane Wizard and Tesla x104, though at the cost of weakening DEF stats.
*Big Bertha's Cluster Bombs Xtreme costing more while Dragonbreath Launcher costs less AND deals more damage.
*Tesla x104's Overcharge dealing less damage. Given that Overcharge is a powerful incomparable aspect, it works out just fine.