Level four is like a steroid induced football player who worked out his whole life for some people including me. The best tactic is just spamming a huge amount of lairs and traps to kill each specific enemy. I don't know, it helps though.
On the next one, you should make it so the player can take over camps or cities and recruit soldeirs. And make the camps more spread out on a bigger world with more cities and towns. Including more than one campaign quest.