you need to make the "battle" button more accessible. i was completely lost and couldnt even get the game to start for quite a while after upgrading and im sure a significant number of your missing stars in these ratings (although most are quite high obviously) could be because of the fact that people couldnt figure out how to get the game to start after purchasing upgrades or units.
i have 400 dollars and have the tesla boat upgrade but i am unable to buy it - im not sure if there is any explanation for this but if i have to progress to a certain point in able to buy certain units then i shouldnt be allowed to purchase the corresponding upgrades until the unit can actually be used. if this is because i already had a special unit, then it'd be a lot cooler if i had some kind of an explanation for the fact and/ or how to remove that unit from my fleet so that i can use another. if i can buy 3 more scouts then i should be able to buy 3 more tesla boats unless they are gigantic or something and dont fit on the screen.
didnt really keep playing this... it's just really clunky and didnt make a lot of sense, and i had no control over the combat (which seemed to be a cakewalk despite some people here commenting that it was extremely difficult)
maybe it gets harder in later levels but im kind of disappointed that i spent all my money on something i cant even use and im going to move on to another game now.