I just finished the demo, and it was amazing. The slow pace of everything may be frustrating at first but it made me think of my actions before doing them, and it ended up making the game pretty immersive. I also learned to control the submarine with confidence!! It felt very rewarding, I'm looking forward the full release and I'm really curious of what comes next :)
One thing I'm expecting from the full game is that it will also give you all the time you want to play, without time constraints and active threats, if that makes sense. Playing the demo felt like I was always in danger and I had to hurry up, but at the same time I knew that I could take things slowly and play however I wanted :P