The way I bet the Divide Challenge: Max out all your talent tree and put all the remaining attribute points to building fire rate (I had 213 to spare), nothing to champion (mine was lvl 52 warrior). Then follow the strategy with the Shock Tower, as others allready said. Build one Guard Tower near the entrance and a Battle Standart next to it. Fill the other places as you wish. Build a second BS as soon as possible. Level up both BS and GT until you get 0 fire rate to your Shock Tower. Build two more GT next to it and enjoy total mayhem! Quick fire rate brings quick level up. +30 Waves, Double Enemies. Hope it helps
Anyone who said that nothing has changed here got a big fat (-). Personally I don't understand why.... All they tried to say is that this is not a new game. Almost everything is the same, even the soundtrack is the same! OK, the spy character is great now, but the lame restart system is not and I had high hopes for it....I rated City Siege 2 high enough 4/5, not this time though.
I for example managed to beat 1-10 , 1-20 , 2-3 , 2-9 , 2-11 , 2-13 under par (got lucky on some...!). If someone did it on other levels please post, it would be great help!