Hint: get the rage injection ASAP. If you have 2 bosses on one level, shoot they both with the age injection and you can get them to fight each other, and shoot at them both when they are distracted. Also works with large hoards of zombies, shoot one of the ones with the gun with rage. He will clear half the group for you!
Detector also very useful to get early on in the game to help complete all levels and see where large groups of zombies are
Good game, but becomes a bit of a grind. I finally got the last achievement, took me 7 and a half hours of play time on the easy setting. As people have suggested, being able to see more stats would be helpful, and speed up button greatly needed!
Tip: If you don't want the chore of defending your outpost from attack, you can leave it, do another mission, and then defend it later on foot. You wont lose the area from not defending, just makes the threat go up a lot. I find it a lot easier to defend on foot. Plus, if you have militia and upgrades in tower defenses, the threat decreases slowly over time anyway, without you having to do anything.
Easy way to win the 'Ultimate Rebuilder' badge.
-Start off on easy, train up 5 survivors max for all skills.
-Get the heliport and complete the game through that method
-Send off your 5 max trained survivors and start a new city. It then should be easy to rebuild etc
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