I bought this game on sale, thinking "Eh, 4 dollars, what's the worst that could happen?" Turns out the answer is "a lot".
Before writing the review, I completed the campaign, played some Death Lab and Survival.
Lacking. There are keyboard shortcuts, which is a plus, but the amount of micromanaging is just annoying. There is no way to give your squad very basic commands like "walk over there, but hold your formation" or even "guard here, look a little bit left or right occasionally". I mean, yes, they aren't trained soldiers, but come on - that's very basic "use your brain to survive" stuff.
Variety / Difficulty / Replayability
Personally, I found it too easy. Take an easily defendable position (beware windows), shoot single zombie, run back to squad, profit. If there are hearts, use melee and sneak your way through. After the hearts are disabled, progress as usual. As this works almost every time, it also gets repetitive. New equipment isn't a necessity, it just achieves victory faster.
The different game modes. Yes. Campaign is as described above. Then there is Death Lab, which I actually liked. Kind of. It, too, got old pretty fast. Survival mode is a joke. I kind of expected it to be like the campaign, just without the story and a larger or procedurally generated map. Turns out, there are no branches, no loops, no nothing - just node after node, going in a straight line to the right.
So, is the campaign worth replaying? After all, the store page promises random elements. And again, no. While it does, in fact, randomize the campaign map, the actual nodes seem to draw from a pool of predesigned maps and/or houses. While this in itself isn't bad, there are just too few of those to keep things interesting. Even halfway through my first (and only) campaign playthrough, I never encountered any new layouts (excluding the "story nodes")
Just look at the forums. Also, I played this game some months ago, and the bugs are still there. Chances are they will never be fixed, with the developer disregarding bug reports and calling the game "finished". Again, read the forums for details on this. I can just list the bugs I personally encountered. They range anywhere from "minor" over "annoying" up to "gamebreaking".
-) Gamebreaking: Rescuing more survivors than you have space for locks you on the "send survivor to city" screen.
-) Grabbers and Jumpers don't care about walls. And by that, I really mean WALLS, not windows. I encountered this many times while defending, but I is especially glaring with the survivors hiding behind the "hidden button" doors, suddenly being surrounded by Jumpers halfway. And yes, that also happens before the button is pressed. One time, I actually watched them glitch through the door (Apparently, they cared more about the locked-in survivor than about my squadmates standing directly behing them).
-) Once hunger and bug-related deaths start to fill up your graveyard, it is virtually rendered useless, as there is no scrolling.
-) Many more minor stuff (like the game randomly unpausing when giving commands), but really, I won't list them all, considering the much more major bugs.
Survivors / City Map / Resources
Good idea, but IMHO, poorly executed. The resources themselves are sparse at first (not a bad thing!), but around the early late-game, they are completely useless. Except for food, of which you will not have enough. By far. Ever. You will have way too much of everything else, mainly because the blueprints drop much faster. By the time you first have enough resources for the first firearm blueprint, you will have found much better ones. Even with reasonable mid-gear upgrades, your squad will have the best equipment far before the campaign is over.
The survivors... Apart from attracting more zombies on heart maps (IMHO the only difficulty spike over the course of the campaign) they are useless as well. When they don't break your game (see "Bugs" above), they idle around in your cities. "Idle", because it is very easy to avoid the zombies attacking back. In fact, the only time that happened to me was when I explicitly wanted it to happen (Achievement! Yay!). And even if they WOULD need to actually defend your cities - chances are they couldn't. Remember what I said about food a little bit earlier? When you run out of food, survivors die. Seems logical. BUT: The dying survivors are NOT selected randomly. It always hits the most recently rescued ones. Chances are pretty good that those are the survivors manning your cities on the front, leaving them empty.
Graphics / Sound
Very good. The graphics fit the gameplay, the music fits the situations, and... yes. Short review, but that's all there is to say about it. I especially liked the Death Lab BGM.
So, the summarizing question: Knowing everything I do now, would I buy the game again?
No. Plain and simple. For reasons, see everything above.