Wow! Thanks a million for the great feedback.  I'm glad you enjoyed my little game.  It has its rough edges, yet I am very proud of it as a one person team.  The feedback you provided makes my day and is very constructive.  I can answer some questions:

The Gun Level:
Each level you do more damage. Off the top of my head I think it is 4 shots to kill a deer on level 1 yet only 2 on level 2. Level 5 is the cap.

Saving:
Believe me - I want a save.  It was my first time working with GMS2 and I laid the whole game out and when I went to add the built in save, loading the game again literally broke all the depths on the instances making all the menus behind the player etc?  I will need to build out a save function from the ground up and refactor the way some of the variables are setup.  Bla Bla Bla Dev talk, yet it has made me super sad to not get it implemented as it is 1000% needed for the game.

Running:
I had it implemented in the early stages of the game.  Would be cool to have a reason to use energy and also you could get more hungry after running a lot.  All ideas.  I might revisit this.

I'm really happy with your kind words here.  I have seen you on my Twitter feed.  I will continue to check out your work there.  I'm pretty relaxed around game making and sometimes use it almost therapeutically.  Life is Short = Be Creative !

Thanks my Friend :)