hehe I have lost a few more hours
Yeah, ranged attack with choke points is the key. If there are two entrances I find it best to work out which ones are more likely to have armour and put mage towers there, and put cannons for mobs with magic defence at the other entrance. I usually put two cannons or two mage towers at the entrances to do as much damage as I can.
Guards do the least amount of damage but will hold things up but dont use too many of them. I learnt that the hard way
Grave sites are best dealt with by having ranged attack on them, a rangers tower and a cannon. Always soften up your enemies before they meet your soldiers or they will walk straight through.
And yep some sort of ranged attack at the exit to get those few stragglers.
I am really struggling with the last level, I get to wave the second last wave and I get smashed. Damn necromancers!