The idea of goblin saboteur infiltrating enemy base is clever.
I appreciate in-game tutorial.
Game is hard - I understand it is as designed, but I didn't had enough patience to get past the enemies on second level (and oh my - how many swear words were yelled :-D). It might help to lower the stealth cooldown - especially when you can still wait for it to replenish, but there is no fun in waiting. Or maybe if the enemy spotting was not insta-death but you had some time to escape the view cone.
Visuals and sounds are lovely.
Overall - great job!