I'm so impressed with this! Great gameplay, great concept, and great presentation.
Having a stealth element combined with the monster killing process was great. I also liked the way the shadows were done, both offering a way to hide from the enemies and a way to obstruct your own view. It really felt like I was stalking them. Also, having the attack jump forward means that I almost always landed attacks I tried, and it can serve as a getting away mechanism as well.
The bigger phase was less fun, as it was essentially just mindlessly spamming attacks and seemingly infinite armies. I would have liked to see it scale up slower and maintain some form of stealth, or at least some way to defend yourself against the enemies other than just attacking.
Also, and this might just be a preference thing, I wonder if a slower pace (for the first phase, I mean) would have helped build the tension and the feeling of stalking prey.
But anyway, loved this; absolutely incredible work. Well done!