On map 2 with the tower in the middle, there is a problem. On successful by me, it 1st turned red then blue and spent the whole time shooting at both sides and produced both red and blue archers.
The combinations can be found here
http://www.towerdefence.net/index.php?page=page&pid=40
and some mazing idea here
http://www.towerdefence.net/index.php?page=page&pid=41
Oh and 1 more thing.. Since 'difficult' and 'tough' mean prety much the same thing, 'very difficult' and 'very tough' are not good indicators of a levels difficulty.
Harvesting is easy, place 1 or 2 units close together at each end of the route. When each wave starts, harvest with units near the end of the route and switch to attack as the mobs move into range at the same time using units near the start to harvest instead.
Items can turn the tide in your favour, a unit with a powerful single attack could use a splash item or a unit equipped with a splash weapon could be more effective with slow, damage, speed or other. It is sometimes better to build and equip a unit that can use an item to the greatest advantage then to give to a unit which has no need for it.
I really like this game, finding the right strategy to beat each level is challenging and fun. Harvesting adds some micro-management, choosing units, placement, weapons and who to give items to not to mention getting the the right skills before you even start makes it more then a simple tower defence.
Only annoying thing is equpping an item means you can't unequip it and give to someone else. Also if I decide to change a units weapon or equipment like a mage I can't give the old stuff to a new mage I have to recycle it instead. Also I got a bug 1st time I played where an info panel for an item bugged and I had to finish level before it went. I'm looking forward to seeing how this game evolves.