ObAK (Classic)

The valve section is a bit annoying because you have to step away from the valves to see what they've done. I see you have little counters on the machine, you could have a display counter for each pipe then have them display if they are on or off.

The stones need some sort of indicator. Maybe even allow us to carry 2-3 at a time. It would make it less repetitive to recollect stones.
The lock on the bars needs to be more visible as well, maybe even lighter in colour so it can be seen better.

I would change the door opening trigger to the whole door and not just the handle, it can be too exact and it can be a bit bothersome sometimes. A good middle ground would be just to increase the detect zone around the handle so it's in view.

There is a few things that I think could improve the game. It's solid and can be finished it just needs a few tweaks, nothing major.
Consider adding a candle or some highlighter on the key in the skeleton room in the beginning. I barely noticed it.

MORE. Creepy