Killer Bug One
No matter what, everyone wanted to head straight into the airlocks. Due to a combination of size and mesh issues, the player would get trapped inside the mesh and be forced to restart the game. Obviously this is a huge gameplay issue as the airlocks are key to the narrative of the game and its never fun to find a game killing bug. It may be worth resizing these or rethinking how they are implemented in the game.
Bug Two
I realized far too late that Unity really dislikes planes and very thin polyshapes. Many of my objects lost their faces when playing the game and this created transparent walls and surfaces the player could just walk through. Another game breaking bug in some instances, as the player could get trapped or lost. And generally, aesthetically it was rubbish. This was easily fixed by duplicating the shape and turning it inside out. Still, the feedback gathered consisted a lot with mentioning this. It created a very 'Unfinished' look.
Positives
There were positives to come out of this prototype loop, that indicate I'm moving in the right direction. The art direction was mentioned in a positive light - there were quite a few comments stating that the level was immersive and created a certain feel. Others said that it seemed like an interesting environment to walk around in and explore. It's just a huge shame that many of the key elements caused game breaking bugs.
Reflections
All in all I'd call it a successful day. I had a few important bugs discovered and got some reassuring feedback in terms of art direction. The structure of the map needs changing for sure - A lot of players got tempted into areas that I wouldn't necessarily of liked them to head in to. Its also worth considering expanding the play area on to Mars' surface. This would give another unique visual experience to the player. A lot to think about and a lot to do.