Let's trade feedback. I submitted a project too.
- Mechanics: Your upgrades and overall design are good. I don't think you need half's and decimal cost points though. Using whole points would help support kids to play this.
- Appeal: I could see this as a mobile game. I like the theme and it's quick getting into the game. Simplify the UI and I think it could work well overall. On PC, the mouse makes this easier, but on mobile I bet it can get addicting without relying on mouse moving. Do you have plans to expand?
- Art Style: The alien invasion theme is easy to build on. I know your aliens vary by color and ship but it will be interesting with even mores hips, aliens of different heights and even mini small ones that are even harder to hit.
- Recommendations: Look into Time Crisis games. I think they have a mobile version too. It's a cross-hair shooter game too, look into how they vary simple enemies and that even the enemies interact with one another in good and bad ways. I think this game could use a Bumper cars effect or enemies that can bounce off of each other. After a while there's a lot of enemies---it'll be even more enticing if they bounce and repel each other. For shooting, add maybe a charge or stamina bar for when the next shot can fire, because the time in between shots is very noticeable at the moment but not shown in UI well.