This was fun to play! The impact of firing the gun was great, with the sound and the camera shake. I felt like you tuned the movement well, as it didn't feel too stiff. I really appreciated the attention you gave to the UI and pickup system. It was very well done! I would suggest getting a few different sfx for different guns, so that it won't be as repetitive. I also noticed that some items in the environment (like rocks) were destructible. That's a nice touch!
Also, you might have been choosing a random tile for the enemy to spawn at. When this happened to be right in front of the player, it felt a little unfair. Maybe you can add an exclusion zone around the player spawn? It sounds like you are going to keep working on it, and I'm glad! It was fun! Great job :)
And what a craaaAAAaazy and colorful guide screen. I loved it!