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Zombie City Defense by Mozg Labs is an Android game that runs well on my Moto X (first generation). I don't remember exactly where or who recommended this game to me, but I am glad it happened. This is a game of tactics. You command each of your units (each with different attributes) to kill all the zombies. The goal is to survive. You can either try and take over the map, but this may spread your troops too thin and they be unable to hold their ground. Or, you can guard a small area, but run the risk of running low on resources. The tactic is all up to you. There are a handful of maps (with more released with each app upgrade) and three difficulty levels, more than enough.
I completely love the gameplay of Zombie City Defense. It allows my full range of strategic decisions. The map is a cool 3D style with a surprisingly simple method of "moving around the map". Most of the time, I find it a better risk for early expansion to gain the most resources and unit upgrades. Often times when I simply hold my ground, I find myself being overrun by Zombies due to insufficient funds to upgrade or build new units. There isn't a way to force a saved game, but the game does automatically save your progress, as each game can take 30 or more minutes to play.
While in the midst of a game, I sometimes wish I had a tablet with a larger screen, as are lots of details happening in multiple locations that the advantages of a larger screen would improve the overall gameplay experience. Also, telling units to "search and clear" a building is sometimes unreliable and I find my units sitting right outside the building (without cover). The part I dislike about this game the most is graphics of units are a collection different shapes. I don't mind the buildings being outlined shapes, as its necessary to see behind buildings, but trying to keep straight what each unit is based on a shape is both challenging and unnecessary, especially for a game that is not free ($2.49 USD).
Other than that, the learn curve for Zombie City Defense is quite high. But here are some step by step instructions for those learning the basics:
You choose 4 infantry types and 2 vehicle types you want available for you on the map. You can also choose special upgrades (only active on the one game), but that will cost you points.
A green building is one that has been fortified. This means any infantry unit inside will gain a defensive advantage. A blue (neon) building is empty, and simply needs to be fortified (this takes time, depending on the size of the building). A red building has zombies insides which will pop out when you enter. Once all the zombies are cleared, it becomes a blue (neon) building which then needs to be fortified.
Each building may the have icons on top. The square box icons indicate they produce resources for you. A house icon means for a limited time, you can save people who can be trained as infantry or to command a vehicle. The bullet icon means the building contains a lot of resources (once fortified). The circle icon indicates your HQ, which must be protect at all time. If zombies take over your HQ for an extended period of time, the game is over. The gas mask icon indicates where you train infantry and the tank icon is where you build vehicles. Buildings all require a unit to be inside for it to be active.
Some infantry types gain advantage from being inside tall buildings while other will gain advantage from being inside blue (neon) buildings. Other infantry types are better suited to clearing zombie buildings, and other infantry types a more efficient (twice as fast) at fortifying a building. The one infantry unit you get on every map and cannot be swapped out (and took me a while to find) is the Engineer that can be trained at the HQ. The engineer will double the output at resource buildings, but have no defensive abilities.
Both infantry and vehicles can be upgraded, but individually. This means if you train two snipers, you'll have to upgrade them one at a time (instead of upgrading the sniper class as a whole). This is why having a stead flow of resources is critical to winning the game.
The description for infantry and vehicles are available and precisely describe their abilities, so I won't go into detail here.
You don't have access to every infantry type when you first download the app, but you can research them instantly with points you gain from winning a map. So use the points you gain carefully, otherwise you can by more points with real money.
And that's the main detail of the game. If the developer at Mozg Labs of the games ever read this, I do hope that they end up introducing graphics. That's probably the main reason I ended up quitting the game is because the by the time I realized what I opponent I was up against, my army was severely crippled. And all because I couldn't quickly figure out the enemy (especially since they often come from all sides). Other than that, I love the game.