Pretty cool game!
Only played one time part way through. It is pretty rough not being able to change the order of units once you place them, but can see how that makes it a big part of the strategy once you know what kind of units will be available.
At certain times it seems a bit unclear on what to click on or what you can click on. Took a bit to realize that you could upgrade units. Also, never really understood the freeze and the interactions when clicking on the units to buy.