Great work, I agree, it's very polished. I love that the game is suprisingly playable solo despite being a 2 player game thanks to the unique mechanics :)
I found myself typically dying after forgetting to reload at the right time. I'm not saying you should adjust the difficulty, but personally I think I would fare better if there was a feedback (like an empty 'click' sound) to let you know you're out instead of always referring to the UI in the corner.
The enemies are well designed as well, you can tell they will be tougher just by looking!