Hello!
I just played through the demo, and I thought it was overall a pretty good experience. I did however have a few small issues, with some parts of the game:
Firstly, it was somewhat hard to find out what movement state I was in, when it came to wallrunning and / or climbing. Besides the sound effects, it could be hard to see whether I had grabbed onto a ledge, or was about to slide down the wall. As a possible solution to this, I think it'd help a lot if it was possible to see the player's arms, or something like that, to help determine if a ledge is grabbed or being scaled.
Something else that didn't seem to work very well for me, was getting out of water. I'd swim up to the ledge, and try and jump / climb out of the water, but usually it would only result in me jumping a little out of the water, just to fall back in. Maybe I missed something obvious, but it seemed to be a little random whether I could or couldn't get out of the water. Another small note to the water: It'd be nice if you could just swim in the direction you're looking. For example, instead of pressing space to get an upward-burst in the water, it'd be nice if it was possible to just look up and then hold W to swim upwards.
Lastly, and perhaps most crucially, aiming just didn't really feel that good. The weapons themselves were great, but aiming felt sluggish due to the weapon / aim lag. It made it especially hard to move and shoot at the same time, or even just flick over an enemy and actually land the shot. Perhaps there's a reason for the aim lag, but I felt it was a large drawback, and should at least perhaps be made more snappy or quicker.
Otherwise a very nice demo, and I look forward to seeing more in the future :^)