I think it needs only a few things aside from more levels, to make it more fun. First off, a replay feature. I think it would actually work better here than in superhot, as it's already kinda cinematic. Second, I think you need to tweak the death animations, as they're quite boring. Take a cue from hotline miami, and vary them up depending on weapons, and they'd be fine. Finally, the blood. I don't know if it's intentional, but the way it looks now is quite unvisceral, which I think this game could be quite easily. Other than that, great job, and I look forward to the project's completion!