Hi! Thanks for playing and for the detailed feedback!
There's actually upgrades after wave 8 completion that makes it a bit more interesting, but I totally get the need for more. I planned to add a grenade weapon exactly for this scenario but unfortunately had no time to do that :(
The green bug screen bug is a weird one. I actually stumbled upon it minutes before the deadline so it was too late to debug that. I think I know what causes it though
EDIT:
I believe the green screen is when the game's screen is selected and highlighted in the browser, probably because of holding and moving the mouse - it happened to a friend of mine during testing and he said clicking outside the game's screen solved this issue. I think constraining the mouse to the game's screen will probably solve this bug in a future update.