thanks for the feedback.
1. Did you play on web? Because performance is way better on PC.
2. gigantic zombies: There is a 5% chance for a zombie to get gigantic. there are also 3 bosses. When did the zombies start flying? Try the pc version, i am sure you can manage to survive 200+ seconds. :)
3. too dense foliage: there is a road on the ground. Just follow that, you will soon be in an area with much lower tree density :)