Too hard w/o mage spam
I liked this game, I really did. I only have a couple issues. It ticks me off that the higher ranked guys don't keep the skills of the lower ranked ones. Another issue was either you or the enemy boss unable to attack without magic, resulting in a mega quick loss or victory. Also, the game is incredibly hard to the point of sh*ting yourself. The way I beat it was max upgrading earthquake, getting the level 2 rock talon power. Then in a battle, max out your level 1 mages in the beginning (if you have the mana orb thing you'll have 400 mp) and in the very beginning use the rock talon. Then EQ and stone throw the boss. Repeat for every round, and fully upgrade 2 of the mages to max healers asap. If you want, you can spend the extra upgrade points you'll have on the protection cloak, and use that on your two super mages when they're up at the boss. This method is practically flawless, and turned my absolute crap stradegy from before, into absolute win.
However, to make the game better:
Increase the power, armor, etc. etc. off all non mage units. Decrease the cost of them all slightly too. Then, decrease the effect of the level one mages, or just shift it to a level 2 or 3 ability, seeing how good it is. Finally, decrease the power of any and all of the magic abilities that hit every enemy on the field. All of these things together will better help stabilize this game. :D