Hi, this is Matthias. In response to your questions:
1. I lasted about three minutes once I got a handle on the controls. I felt like I was playing a game that was medium to medium hard.
2. In the beginning, there were enough enemies that I could handle. Near the end, I was ganged up on by a horde of enemies. For the final build, I suggest that you tone down the enemy spawn rate.
3. I felt that swapping arms was intuitive and smooth. My only complaint is that the arms don't respawn, and there are a limited amount of arms to use. I know this is still in development, but its something to consider.
4. The controls made sense and were really smooth. The only thing that I would change is by making the space bar be shoot, and the right click be switching out the arms.
5. The UI was very clear. I knew how much ammo the arms had as well as how much hits I had left before dying.
6. I thought the art style communicated the game well, but I found it hard to gauge where the enemies were, as they spawned outside of my field of view. I think either a minimap or pulling out the camera would fix this issue.
7. The only bug that I encountered was that you have the mouse location be where you are aiming your shots. While this might work for a FPS, it confused me as to where I was shooting. I believe that the character should shoot according to where the arm is pointing at.
That is my response. Good Luck!