Thanks for playing! You made a lot of great suggestions for improvements.
I also want to do things like render the letters above the zombies' heads on a separate layer and capture them with a second camera before compositing them with the main camera. At the moment, the letters can sometimes be obscured by environmental objects, so having more control over that would be useful.
The play area could also benefit from some verticality, although that would need a lot of playtesting to determine whether it actually improves the gameplay.
The electric sound effect was added to the line renderer, but it should really be attached to the zombie game object instead. That's why it's currently too loud (and a little obnoxious!), so that's something that definitely needs to be changed.
Thanks again for playing and for the feedback. I'll work on getting it updated into something even more playable!