I just destroyed all zombies in the whole city, got all buildings I could have, turned every useless building into smtg useful, completed all ways to win on my city, now I have nothing to do. By the way, did anyone call your city Raccon City?
A good group is: zombie, healing crystal, succubus, dragon rider, yetti and magic cannon, because: zombie: holds enemies. hc: heals. Succ and mc: holds revenge waves. dr and yetti: make real damage
The only thing I think is unfair in this game is that if you´re holding a revenge wave, they keep putting one after the other, and the enemy's army sometimes gets to the mark of 100 units.
The goblin card is good even counting their weakness, because you can make a big pack with them fastly, so they are very good as scouts, of course it's not possible to hold a Yeti with them, but the weaker units are fine. Of course, if your enemy has the ghost armor or the bomber, they'll kill them very fastly.