One of the best games I've played in a while. Really great job, I can rate it 5/5 with clear conscience. Then again, I'd love to see some extra things in the next game. More upgrade tiers, the ability to change race, or choose it at the beggining - or maybe unlock it as you progress/earn achievements? Also, planets with some extras, and obviously - AI tweak, since now it's too basic - they only attack what you attack. Anyway, this game is awesome.
Infernal Magnet is well underpowered, especially concerning ninjas. If TOUCHING your gems means you won't get brilliant, then you might as well not care if they are stolen.
The less money you spend the better your score is. Try to look at the score indicator during the game. Each time you buy new tower it goes down. You get 3 medals if you score at least 70% in levels without shooting spiders. Than calculation is more complex, but it is always about spending as little money as it is possible. This should encourage you to plan your strategy very carefully.
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Thanks!)