Well, great game! The car movement felt great, bumping into zombies with chainsaw was fun.. I had fun :D
I will critize some parts a little bit, i realise this was a game jam with time pressure and i must say, you did a great job of compleating a fun game under such circumstances. I am just critizing the game like it was a long project..
1- The ai is really not useful. It dissapeared into thin air and when i finally found it, it was stuck on a wall. Now, even if the ai was better, considering this is a themed game jam, it should be close to the player, so player can actually see the ai killing zombies. You know, it can kill zombies on the other side of the map. But how could player know that?
2- Tower hp problem. :(
3- 5 towers is a lot to defend. Maybe you could make the map a bit smaller with fewer towers but with a lot more zombies to balance the difficulty?
4- Okay i am nitpicking rn. The graphics is obviusly 5/5, i will rate it that way. But i just want to add this.. The ground textures tiling is very obvius. Main ground textures should lack details which make it obvius to detect. Like colors should be extremely similar. But, since we still want some detail on the ground, you can make few textures which are very detailed and one main undetailed texture. Since you obviusly used unity terrain system, you can actually paint textures on it. You should paint detailed textures on top of the main one in a way which does not make it look like it was tiled. Also you can change the tiling and offset of the textures, that can be useful on some occasions. Ofc spending time on this would be a waste of precious time. I am just adding this because i think you cared about graphics while making this one. In case you wanted to make it's graphics even better you can try to implement this.