Hi, I tested it for a while and here is my feedback:

• It's a nice arcade, fun to play to just sit and relax
• the sounds and visuals are nice
• Input has some issues. I can only shoot when I don't move which is very annoying.
• The collision of the character seems to be only on the lower half. When I get the green dot, I have to step on it with lower half of the body. It's bit counterintuitive.
• Some kind of points would be nice: how far you get or how many enemies you've killed.

Keep it up, it looks promising! 

If you find some time, it would be nice if you could look into my idea and share your thoughts about it: Lua Playground