I like the low poly visuals, and while there is not much variety of effects, they are good enough.
Only real issue I would point for controller users is to be able to pick upgrades with the controller, at least with just a button, since I did had to grab the mouse again and again just to pick another upgrade 10 seconds later.
And also, I am grateful for the small countdown right after picking an upgrade, so you can get ready again, not that many games do so.