I prefer spamming upgraded Swordsman, alternating with a Spearman or Scout occasionally. Allows me to win a little faster if I have a few faster recharge, faster speed units mixed in.
The AI needs to alternate strategies better. Have it spam faster units if the person playing is doing that as well. Then again with this game patience is the winning factor a lot of the time.
In addition to the Charge feature, maybe have a Earthquake which lightlly damages all enemy units and scatters them on the map. That way the AI could break spamming occasionally making it a little harder.
Laggy even with a good computer. Game mechanics break easily as well. My arms detach from my body half way through some of the levels. It's actually kind of funny. The first boss is too laggy to complete. Badly programmed. They need to pick more original, stable games for challenges.