I second everything Szym said. The base ideas here are cool and could produce a very nice puzzley game, but as is there is a lot of frustration.
I love the idea of preventing backward movement, and the randomness of your moves makes sneaking around more tense which can be cool. The theming is great, and I like the pixel art.
What I would recommend adding/investigating:
* Try removing the randomness of the guards movements. Keep the randomness of the player movement, but make the guards predictable. Maybe have a visible effect to show where they will move next turn.
* Zoom out the view more, or provide a way to move the camera outside of the players own movements. It can feel very unfair to pop out where a guard is who was offscreen and you had no way of knowing they were there. Giving me a way to see where I will be going would help that a lot.
* Movement hurts my eyes. The jarring jump of the entire world on each tile is not pleasant to look at. Having a smooth movement and some animation to it would alleviate that, or having the camera zoomed fully out so you see the whole level and it never moves may work as well.
* Change the music. For this kind of contemplative game, you want something that is present but doesn't draw a lot of attention to itself. This often happens when there is a lot of repetition of harsh noises. I'd recommend putting it on in the background and listening to it at a normal volume while you do other things. If it doesn't annoy/distract you, then it is usable as background music.
* Don't have a single tile wide hallway open into a guards path. This feels very bad when you are forced to walk into the guard.
* Clean up the background pixel art. A single floor tile shouldn't be so busy as to draw attention to itself.