After LPing this, a couple more save spots near the bottom could have done well. I really am amazed by some of the tiles used, as well as the challenges presented.
Graphics: 9/10
I don't think I've seen any default tiles at all, and for custom objects to replicate water, you're pretty good with custom stuff.
Challenge: 8/10
Pretty hard stuff. Fits the hard tag very well, but is possibly borderline very hard due to a few save points lacking. (Overall, you had some interesting things on the route up. I actually had to strategize my ascent.)
Music: 9/10
It seems to be very fitting for a watery dive.
Overall: 9/10
I approve of this level. I can't say much more.