I killed the giant by throwing everything at him all the time. If you actually want to get all strategic though, you will notice there are certain times when you can damage him and others when you can't. So just throw everything at him when he's vulnerable.
This game is really really boring. After the first level, nothing changes. Everything takes to long. Buying units is a waste, since then you get less cash (less income and they cost money).
I can't seem to get the social network badge. I beat the game placing every unit on the map. Am I misunderstanding the badge? Its just place all 5 unit types on a map right?
 "Wake Up the Box 2"){kind=icon}
 "Museum of Thieves"){kind=icon}
 "Fujitsu Defender"){kind=icon}
 "One Button Bob"){kind=icon}
 "VVVVVV Demo"){kind=icon}
 "Cover Orange 2"){kind=icon}
 "Factory Balls 3"){kind=icon}
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 "Balloon in a Wasteland"){kind=icon}
 "Bowmaster Prelude"){kind=icon}
 "4 Differences"){kind=icon}
 "Defend your Honor!"){kind=icon}