Great game! Here's some UI suggestions:
- Adding more hotkeys, ex: C or Spacebar to confirm, Esc or E to close, G to toggle the grid, and the number keys for selecting upgrade types.
- Selecting E from the Esc menu switches to edit mode.
- Scroll wheel to cycle between upgrade types.
- Click-dragging from blue squares to the edge to preview an upgrade, and then releasing to apply upgrades, or maybe adding the WASD keys to apply upgrades?
- Basically it would be nice if I didn't have to move the mouse around the whole screen to do edits.