I've been playing this game all week and it wrecked me like a dying hooker with a heart of gold and pregnant with the third child. But maybe I relate to Tower Defense games in a weird way.
There's so much polish here for a game made by three people, the illustrated graphics of course grab you, but this title does so much to flourish this genre's craft, it's like the oblong cousin of Immortal Defense, doing what you would expect, only much more so.
Where to begin? Upgrades are a fiesta, just shit tons of upgrades. Each tower level is like another layer of an onion, fresh art, faster speeds to go with the damage, a viscerally more significant impact, this part is quite well balanced. Magic towers seemed disproportionately power compared to arrow towers, given that most enemies don't have magic resistance but many do have armor, but ok. When you get towers to level 4, you get to choose, and each choice not only affects the vector and speed dynamics of the projectiles, but what further upgrades you can chose. Upgrades also seemed a bit overly priced, but you tend to unlock those later in a session where your cashflow is more powerful and power-per-space takes a premium. The most interesting twist on the genre here is that there are no slow towers per se, rather you buy barracks to house soliders, and these soldiers rather than slowing a radius of enemies by a certain quotient, will stop a finite number of enemies indefinitely, until they are killed at least. There are two global intervention powers that keep you engaged and make up for the lack of a fast-forward: call reinforcements which acts like an instant (2) soldier spawn - 10 second cool-down, and Meteor which is you trump card - 80 second cool-down. The balance takes the typical spend-and-wait gameplay of TD and makes it vivid; it also doesn't hurt that the game is full of pithy references to other realms of geek culture.
Maybe the best thing about the game are the little touches. In one level there is a Slyvan Elf house you can repair and expensively hire expendable Elf warriors. In another, there's a frozen Sasquatch, many players might just think it part of the scenery, but if you bother to throw a meteor there you'll find a nice surprise. The game's full of these little touches and they really drive forward the level design in an inexorable death-march that will kill your productivity in the same way that fear is the mind-killer.