I like it but...I don't *love* it.
Basically, while the core of the game is awesome, everything *past* the epic triple boss fight is lacklustre.
Each enemy killed is worth so bleeping little per that it does NOT justify their health. I would recommend either putting more value on units across the board or make the different types worth more than others. Regardless, that number HAS to go up.
Alternatively, you could increase the amount and rate of which enemies appear and keep the point value the same *but* reasonably decrease each units health proportionately.
Or, as yet another option, you could drastically reduce the pricing scheme for the upgrades. At least you wouldn't have to tweak/balance nearly as much.
Just a thought.
Frankly, when I saw the upgrade system and saw the Backpack upgrades, I immediately groaned and said to myself, "ah, CRAP, I'll need to waste a ton of money getting that to max just to have any reasonable pacing". All before I even played the first level...and I was right.
Once you hit the 31st wave of enemies and onwards, there is so incredibly low incentive to continue when you hit that cliff wall one calls a difficulty curve. Not even legitimately difficult, just artificially so as everything has more health and more units come out faster.
I mean, I suppose I might come back to this a few times later on and see if I can push a good stretch to power through it, but because I'm just repeating the same thing over and over again, it's a hit on the morale.
There's keeping something from being entirely forgettable (trust me, the core game is NOT this) but everything past the main game is just overboard.
By the way, reading your update in the description, there's still a couple things that didn't get fixed *entirely*. I would presume you looked at it but it seems a couple of things still happen, though very inconsistently. Basically, when the bomb-runner unit is barrelling across the screen and yelling, if the level ends, he's still screaming until I hit up the next level. Also, the flamethrower noise doesn't stop at all in the same circumstance. I had to refresh my browser entirely to get rid of that since even going to the main menu screen didn't take it off.
Altogether, a fun game but one I'm somewhat reluctant to go back to just to finish off extras I'm not even sure will be worth bothering over.
Regardless, a solid four stars.