Though these are probably planned features (speaking of which, a planned features list would be nice) I wanted to suggest the following:

-XInput support
-Gun Range Upgrade (not sure if it already exists, I haven't tried to get all upgrades)
-Different weapons

For a list of planned features, you can read the new DevBlog entry that i've just released, it will give you an idea of what i have planned for the game, more or less.

For now i'm focusing on gameplay related stuff, so XInput is not on high priority, but i'll get it implemented eventually, 

While the gun customization is limited for now, i'm planning on adding a bunch of single purchase upgrades (like the extractor) that modify the player's bullets and synergize with one another.

Thanks for the feedback!