Disclaimer: i'm a sucker for zombie games so i might be biased in the review for this game since i just love games which include zombies and they instantly gain at least +1 point in grading.
There is plenty of zombie games on the market and thematic is rather washed out, but for me the game is pure fun. If one played Dead Island than this is similar to what one can expect from the game, but with much improved weapons, handling, physics and fine tuned elements.
Some people and reviews complain about the story. I don't want to spoil it, but for me the story is far from bad one. It isn't great as in Mass Effect, but this game has a completely different concept one should take in account. The story is good and IMO decent enough to keep you going. Plus, the side quest add to diversity of the game and give you extra reason to further explore the city.
The game is rather well balanced and it will go easy on you at start and become increasingly difficult as you progress through the game. Also, skill tree (BTW, there are three different skill trees), weapons and environment options really add up to the diversity of gameplay and playing style.
Technically the game is decently optimized for PC. Yes, there were some problems with some GPU's and CPU's (mostly AMD) but most of the issues have been fixed and they're actively working on fixing the rest.
From audio point of view if one has a decent headset or surround sound system audio really adds to the immersion in the zombie infected city. Screams in the background and soft music adds to the great game atmosphere. Combine that with well designed environment (good graphics) and day-night cycle which cycles between rather dull and slow zombies to aggressive ones which are supported by extra powerful ones which appear only during the night, and you get a great zombie game.
Some reviews point out that the missions are repetitive and most of them is based on the same concept which is go-to-location-X-and-fetch-object-Y. While i agree that missions are mostly of that type, they have enough variety to keep player interested for the game and further explore the game. Secondly, just think of it for a second. I one would really find him/her-self in a zombie infected city there would be rather high demand for brave people who would risk their lives to get necessary supplies frm dangerous locations infected with zombies. For me this makes 100% sense. And third, if one pays close attention to detail one can hear irritation in Kyle's (main protagonist aka YOU) voice when he needs to do a go-and-fetch mission again.
Now, all i have written so far is for single player, and on top of that the game offers a nice CO-OP mode which one can play with his/her friends or random players. Plus, there is a nice multiplayer addition to the game too, which is a mixture of Left 4 Dead and Evolve game. In the multiplayer one can choose to be one of the four survivors or be super powerful zombie. CO-OP and multiplayer are highly dependent on people one plays with, as any other multiplayer experience. If one is playing with friends or good players fun is guaranteed and if you play with trolls or bad players who don't respect CO-OP/MP one will have bad time and a free test of his/her tolerance.
The game has some amazing extra value which comes in form of weapon dockets (ie. gold keys if you played Borderlands) which will give player top tier weapons when reclaimed in the game (1 docket = 1 weapon). And the game has a companion app for Android and iOS where one can play Dying Light in a form of Facebook Mafia Wars where one sends scouts on missions. Great thing is that loot from the missions can be transferred to the original game one is playing on the PC or console!
To sum things up, i would highly recommend the game to any player and it would be a must to those who love zombie games. To be completely hones, i haven't played such a great zombie game for quiet a while. For those looking for numbers, here is my game review roundup:
Video: 9/10
Audio: 8/10
Gameplay: 9/10
Fun factor: 10/10
Extra value: 8/10
At the end, one is killing zombies in many creative ways, and if you don't have fun with it and all you have is frustration from the game - you must be doing something wrong.