Your game feel is excellent, shooting enemies feels awesome and you've nailed the appeal of culling the horde. Many games try it, some nail it, some miss. You're nailing it.
I played four runs, and on three of them I got to the last level before what I can only assume is a boss fight. Most rogue likes first levels are pretty harsh, because they know you're going to find yourself on those first levels a lot. You hone your skills going through these levels repeatedly, mastering your play so that you'll be better equipped later in the run. I don't find this appeal in your game. I find that your early levels are so easy that they don't require a lot of effort, which makes me tune out. Even when I do take damage, I quickly find a health pack and I'm back to maximum HP, leaving no incentive to put in effort. A bonus for not taking damage on a level or some more challenge in the early game could remedy this.
There's also just a lot of levels between me and your boss. It's impossible for me not to compare your game to Nuclear Throne, which was far more punishing, but threw unique content and challenges like boss fights at me in much less time.
All that negativity aside, I was compelled to keep playing, and I plan on trying again. You're already fostering that "one more time" mentality these games live off of. Getting a super strong boomstick or a powerful assault rifle just feels right. I look forward to seeing how you innovate on these ideas going forward and introduce more depth to the gameplay :)