Thank you for your feedback. A lot of the points are very helpful.
A lot of the bugs that you have mentioned are either getting fixed or are are on my todo list. I wanted to release a newer version, but then I decided to add more content first.
The save system should work if you create a folder with the name "save" in the same directory that you put the game (the executable file). Maybe next time I should package the release into a zip file rather than just uploading the executable.
Some systems like using different weapons I probably won't implement. It's a great feature but it's just too much effort for a solo dev. The other features I'll definitely consider.