Try to focus on your first two units because all other characters cost too much until later try to rush with swordsmen I did that beat game on normal less than 3 mins per lvl
just beat game it's great upgrade monument health max gold from monument max miners max giants max (I didn't use the giants last lvl) and swordsmen max beat game in 26 mins
Great game haven't finished yet but I think there should be more upgrades more characters to upgrade and a character for you that can be customized with any assortment of powers and you can play the levels again with your high leveled characters and you can upgrade all the upgrades instead of having some not upgraded more levels also
 "Stick War"){kind=icon}
 "Get Off My Lawn"){kind=icon}
 "Azul Baronis"){kind=icon}