It's nice. Bit of "let it play itself" though.
Can't see barrier's health, which is slightly odd, until it becomes irrelevant. Could also use some "current level" and "next level" tooltip on upgrades, just for clarity purposes, since clicking on a "Increases Main Turret Fire Rate by 40%" doesn't actually increase it by another 40%, but an increment of 10%.
Slightly annoying hit detection, where all 3 of your turret shots can hit the same enemy, who couldn't even survive one of them, essentially wasting 66% of your damage. And it just feels odd to have the game end with time still on the clock, would love to at least have an endless enemy wave till the timer runs out instead of a pop-up that blocks auto loop.