The enemies drop power ups for shields and lasers:
Bronze: 1-hit shield / 2 lasers
Silver: 2-hit shield / 3 lasers
Gold: 3-hit shield / 4 lasers
Also, the formation doesn’t move until all enemies (10) have been created, and you get 500 points for clearing a wave, which also raises a level number.
This is a Unity 4.6 version. I tried a Unity 5 upgrade, but the animations and sounds weren’t working correctly and I couldn’t figure it out. The ships wouldn’t start at the first keyframe position and none of the sounds except the background music were playing.
I’ve also noticed that UI elements tend to shrink and move closer together on the web build even though I include 800x600 in Build Settings. Does the canvas shrink?