Superb.
This game had pretty much everything that a good defense game needed, and then some. The only thing it was lacking was a shop, but it made up for it by the upgrade system which was both simple and exciting. Caught in a mixture of 20 zombies, racing to upgrade my SCAR, that was way more exciting than stopping after each level to head into a shop. The jumping was a bit obnoxious at times, as I found myself getting stuck in between two barrels, jumping back and forth while zombies chewed on me. But hey, it was exciting all the same.
The darkness was what really got me, added way more suspense to the game and made it that much more exciting. It added a whole new element to the experience, and made it far more addictive to play. Who cares about killing zombies in light? Having to defend your only source of light aside from a flash light while zombies came from all directions... that was exciting. It was a new experience that definitely made it far more addictive.
The weapon choice was great too, you really had to think about what to use next in some situations, especially on harder difficulties. I wish weapon changes were easier though, I almost killed myself with the grenade launcher the first time I picked it up, because I forgot that I couldn't just switch my primary with Q & E, which made it a tad staggered when I had to switch between various weapons to kill the hordes. However, after I got used to it, it went a lot faster and smoother, but there was a break in the play. Primaries I found were more important than the secondaries to switch between in the heat of the action.
The night vision goggles were a very nice touch, although I wish everything wasn't so green. I hate the night vision for that very reason, it makes everything way too monotone, but in the later levels when zombies could kill your torch almost instantly, you had little choice in the matter. Night vision was your only sure fire way of surviving, unless you had enough road flares stored up to matter, but those didn't last nearly long enough. Night vision became the only option, and I was fine with that. However, they did have their down side, since all the zombies blended in with the background more and could consume you without you knowing.
The auto-reload left out was a good choice, though I was kind of pissed when I found that if I tried to shoot while reloading, it started the reload process all over again. I seriously spent 20 seconds chased around by crowd of 20 zombies just trying to reload my SCAR, firing out of habit. After all, when zombies are running at you, you aren't thinking about "I hope my gun is done reloading", you're thinking, "Holy shit! Die zombies! Wait... why aren't you dying!?" But hey, that was an oversight on my part, and I did manage to figure it out.
The last level was the hardest, even if you had the most awesome gun ever. I pounded those fuckers with bullets, but the bosses were still there, and my health was still low from the final boss fight. I did manage to get through it on my first try just by firing straight forward and plowing through them, occasionally dodging to one side or the other to avoid them blocking my path, but I thought I was going to die! I left that whole area with about 2% health left to my name, and I only got to use like 70 shots of the gun.
What I would love to see is if you have beaten the game in the past, you could be allowed to utilize the "emergency weapon" from the start, because although it would decrease difficulty by a large margin, it would give those people like me who love to do work the first time and fucking win the second the thing that they are looking for, straight up POWER! Maybe just for the difficulty they beat it on or something, but it may be something to consider to reward the people who would like to replay the game, but would like to beat the hell out of it instead of barely scraping by.
But hey, the game is wonderful, and is nothing short of amazing in its programming and game play. I really hope to see a continuation on this soon! Best of luck!