Thanks for playing and for the feedback! Glad you enjoyed the game and found it scary! Nice job on the 161 seconds with 2 waves, that's pretty good.
The points are mainly for score tracking and potentially comparing them to your friends to add a sort of thing to aim for. The formula is a sum of the
- total zombies killed * 100
- waves completed * 500
- accuracy * 1000
- time survived * 10
For the upgrades, it depends. If you don't do bullet damage every turn, I think you fall behind and have to use more hits to take out zombies as the zombies' health increases by 20% per wave, but honestly, the knockback boost combined with bullet fire rate is a pretty good combo if you pair it with the machine gun.