Thanks for the feedback!
As for 1, I think if there was more time I would probably have an option for aiming where you're facing, or at least making it so that bullets fire the direction you're facing if you're not holding arrow keys - I probably could have done that in the time we had, so that was definitely an oversight on my part.
On 2, as a designer, difficulty is often something I mis-judge, especially for jams where there's little time to get others to playtest. I wanted to keep the game in a space where you're really forced to position the zombies for the sake of watering your plants, but I think the player should probably be able to get away with more on the easier difficulty levels, especially with regards to how many bullets you start with.