A handful of issues. I dislike that being found is an instant loss, it turns stealth into a game of avoiding under the guise of stealth. You need to punish sloppy play, not make it grounds for a game over.
I dislike that raycasting isn't shown to the player. You can't be spotted through a wall but the visual doesn't reflect that at all. I dislike that the guards turn on a dime and lack smooth movement. I dislike that you can't use traditional stealth mechanics like creating a diversion or hiding in darkness. Sneaking up on guards feels weirdly artificial although as a mechanic it works. Default movement is too slow and I can't seem to pass level 9.
Overall kind of lackluster. The Ultimate Assassin series does everything this game does and more.