Well, now you've gone and done it. You've made a remarkably unique Tower Defense game, and that takes some serious effort these days, along with a whole lot of crazy.
Harvest: Massive Encounter is honestly just that: a TD game. If you like TD games, you're going to enjoy it.
So what makes it so unique compared to the others out there on the market, from the starcraft 2 maps to flash games?
First off, resource harvesting. You get nothing for killing enemy units; you're dumped into the middle of an endless field full of minerals. Your job is to mine as many minerals as possible, and survive as long as you can. (With some variations on a theme for different game modes).
The map starts out small, but if you build towards the edge of any one side, it'll stretch out, expanding the minimap further and letting you move farther away from your base. As such, you have pretty much unlimited room to build, but the most dense packs of minerals will be close to where you start off, and the farther from your central base you get, the less efficient mining will become.
The towers provided to you are remarkably few in number for a tower defense game, but they're very carefully fine tuned to be exactly what you need. For example, laser towers have relatively short range themselves, but can be set to focus all of the laser towers in an area to a single, massive beam. This effect can scale to an unlimited degree, and you can chain smaller groups of laser towers together to form an enormous, intricate network of lasers that has immense range and godlike firepower, or break off their power temporarily to wipe out a swarm of smaller enemies that are faster.
You can set your towers to prioritize, deprioritize, or ignore certain enemy types as well, so it's well within your power to tell little lasers to focus fire kill the suicide-bomber style gehenna shuttles, but ignore some of the larger units, while having your eagle class missle launchers ignore the shuttles unless they're the only thing left on the screen, or ignore them entirely, only aiming for bigger game to hunt.
Another really unique feature to H:ME is the energy system. I've seriously seen nothing remotely similar to it in any game before or since. The idea is that you build solar power generators, which create a ball of energy every few seconds. The energy ball bounces randomly between any adjacent point that it can possibly reach, until it comes across something that needs power, and then it rams the target and provides the power required, disappearing from your screen in so doing. This quickly leads to a vast, intricate network of energy lines going all over your base, and energy management becomes vitally important. Having a ton of energy on one side of your base, but not the spot that it's needed, is BAD. Fortunately, you have plenty of very easy to use tools to control your energy flow, such as marking a building as top priority to get any and all energy it needs, or drawing out routing paths to force energy balls to travel along a set path, only being allowed to follow their typical AI programming when they exit the path.
Pretty much everything in H:ME can be summed up this way: it's weird, but in a really good way. It's creative, unique, and it WORKS. It's not just different for the sake of being different, but rather, it's different because it makes the game more interesting and fun.
It'll take awhile to get used to most of the unique aspects that Harvest has to offer, but they're well worth the enjoyment once they've grown on you a bit.
Everything Harvest: Massive Encounter does, it does well. The learning curve is really quite steep, however, there's no plot, no multiplayer, and it's really just one big tower defense sandbox. For what it strives to be, it's pretty much perfect at. For what it doesn't try to be, however, it doesn't do at all. If you don't like TD games, this won't be the one to make you a convert, by any means, but it'll be one of the best TD games you've played if you do like them.
Score: About 70%. It does what it does pretty much perfectly, but it completely lacks a few areas that could make it a lot better still.