1. The length of the days felt pretty good overall considering the current number of activities to do. I made it to day 6.
2. I think the oxygen supply is good. It's not a huge issue most of the time, but if you don't pay attention it can become a huge problem.
3. The controls are pretty intuitive. A quick note: your instructions say you shoot with right click but it's actually left click. My biggest problem with the controls was just finding the right way to activate them. For the steering, I could do it once, but it was hard to tell whether I should be able to do it again or how long I would have to wait between steering (side note, I love the graphic that plays when you steer). Also with the fire extinguisher, I had trouble knowing how close I had to be to the fire to be able to use it. I think having a spray animation or something will make that pretty easy to figure out though.
4. The enemies are a good difficulty if the goal is to make them a distraction rather than a challenge. Having to shoot enemies took about the same time and concern it would take to deal with the other problems. If they're meant to be more intimidating, then I'd say you could up their damage a bit.
5. The item drop rate feels good. It's a nice boost after an attack, though sometimes I end up with more health than I need.
6. I think adding more animations and sprites will clear up some of the confusion as to when things can be done. My biggest concern would be indicating when you are or aren't allowed to do a certain action in some way (see question 3). Overall the game already feels good, it's just a matter of making it clear what you're doing.
7. I'd say the difficulty was around a 7. I only made it to day 6, and I think with some practice I could make it much farther. But the constraints of the different emergencies you have to handle keep you moving, and I think it'll definitely keep you from just playing forever.