Great vibe so far! Who did the music?
One big suggestion I have would be to include the key press next to prompts such as hiding and hacking. It was funny because early on I tried pressing UP to hide in shadows before I got to the official hiding spot, but then for some reason I didn't think to try it when I was actually there - I thought the hiding icon above my head meant I was in a safe spot. It took a few tries before I got it and I worry other people might just give up.
Another thing you could consider is maybe a key to toggle players, so you don't have to only use the mouse for that. You could hover the key over the head of the other player, and the mouse can be a backup if the player is offscreen and you forget the key.
I also experienced a bug after taking out the guard, I got caught not cleaning up my mess but there seemed to be a second reply menu flickering over the first one, blocking me from retrying.
I like where you're going with this!