Downloading now small fish. I will give you my thoughts when I'm done
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Edit: If you want me to be honest, I had absolutely no fun with this game. Here are the reasons.
1. Story. The game is called "The Principality of Mars". This story could be totally awesome. In this case, you didn't even mention it besides the title screen background which is a newspaper that isn't aligned correctly. You pretty much start in what appears to be a hotel, and then you shoot red guys, and on the next level things explode.
2. The level design. The rooms are far too big with what little entities they contain, and a good amount of the rooms are pointless. The level was fairly short for their size (my computer was chugging and I mine's pretty good), and the largeness served no purpose. Also, you had to sacrifice the texture size, which made everything look bland. There was no visible lightmapping, and you could see the seems on most of the textures. I also got a bunch of texture issues where there was some z-clashing. The music also just randomly started in a hallway some way before the first fight on the first level. I recommend starting it when the fight starts.
3. Gameplay. As I said, the framerate was chugging, and when I did fight the enemies (nice texture by the way), they were unrealistically hard to kill and not fun at all. Entities seemed to be placed randomly, and the puzzle at the end wasn't implemented naturally (why did there happen to be boxes right near a fence with an unlocked door, which, by the way, were almost the only visible entities in the room).
This is my honest opinion. If you can, well, turn this around, perhaps test out your levels more, this game will be pretty sick.