I like the fact that the alien AI seems quite tactical. I don't like the fact that the human AI (controlling how your turrets shoot) seems quite stupid. It would be a lot better if you could control how the towers fired, either by choosing a target for each turret individually or assign directions to fire at specific targets, like closest, strongest, weakest etc.
What Delinex said. With maximum mana and maxed out shield you will be invulnerable for 4 minutes if you pump your mana to 400 before charging. I say remove the shield spell, and make the gold gain decrease by a lot for every time you beat a level. When I got to the Big Bang (lvl 14), I could beat it by just letting my heroes spawn and hitting assault. Then I'd go surf the web or something for a few minutes, and get 70k gold for the "effort".
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