For a quick review:
It has it's flaws and once you've gotten over the learning curve and how to abuse the population to make cash, it's a game that is all too easy.
Population is THE most important part of this game, which is the games most fatal flaw. If you have no population u have no money, no money, no army, no army, no population etc. it all comes down to population.
Best starter on hard:
Revenue streams level 1,
+2 salesmen,
Full upgrade both items,
+2 Zombologists,
10 Meatheads, and
+1 Commanders.
With this you should be able to conquer the poles, and most of Africa, once you have the cash (you WILL definitely) buy another 10 Meatheads, the defence upgrade for the meathead and 2 more commanders to conquer Canada with.
Always prioritize, Military>Sales upgrades>Company upgrades, and be 110% sure you can level up your company, it may take a few games but as a basis you should have these continents/countries AND full sales upgrades before leveling:
Level 2: Canada and Africa
Level 3: C. America, S. Asia, 1+ Cities in S. America
Level 4: Japan, Australia, S. America
Level 5: Russia
Level 6: The game is over go home
At first I didn't understand why the unlockable zombies at 13+ (I think) seemed weaker than the predecessors, but I looked carefully and realised that the next 4 zombies get 100 attack and defence in certain regions. Tentacle zombies get maxed attack and defence in Japan, you get them early, their upgrades are cheap (from here on in, all upgrades are cheap as fuck) and it allows you to conquer Japan so easily. Use them on Russia, N. America and Europe, you can see where they excel on the description of them where you purchase X amounts of em.
It's a fun and interesting game, but it has a quite fundamental problem within the design of the game.
ALSO: At first, I was gonna bitch about how you can't add multiple units into your army at the same time, glad you added that hold click feature :S