do get 5 stars on the last map you need a very balanced team. i focused my units on the two path joining places. i used a few good high level wizards and a lot of lower level archers and melee units (which i improved as time went on). This tactic worked for me.
an all round brilliant game, not too hard but hard enough to be challenging and fun. the only thing that lets it down is the stuck-in-the-ceiling/wall-glitch