Dude this is sweet! I love pico-8, and as a bit of a classic 3D nerd (I wrote a paper on ID software and the development of Doom just a few months back...) this really tickles my fancy.
Very impressive what you managed to throw together in pico-8, and it was surprisingly readable. If you continue to work on this for a bit, I think using the dark and light-grey colors would be useful in showing depth and how far away a wall is.
The map is well done too, but you cant exit it after its opened.
While it might not be much for gameplay, you've impressed me in the technical aspect!