There were a lot of interesting concepts in this game. I liked the premise where you do better if you remain unseen, but can still complete the level if seen.
Not being able to clearly see where the enemies were looking made it impossible for me to reliably avoid being seen. I could never be sure where their vision extended, and several times I felt like I got detected from behind crates. Even if you just draw the vision cones, that would improve the feel immensely, because then I can properly plan my actions.
The controls were too slippery for my tastes. I felt like I was skating on ice, which made it harder to move precisely, but that's a valid stylistic choice if that's the gameplay you're looking for.
Overall, good game! I think there's promise in the mechanics you've got.