Its a pretty unique concept.
The enemies reaction time is so fast it gets kinda frustrating after a point (especially with the red sniper dudes that just instakill you if youre in their sight for longer than a tenth of a second). And sometimes even though physically you think you stopped dead theres still some tiny micromovement in your hand that causes the shots to turn yellow and gets you killed.
Think with some polish and maybe a bit of rebalancing itd be quite fun.
Edit: Oh also itd be pretty cool to see a replay feature where you can watch how the level went down after finishing it.