It's good, looks lovely and the animations are great. I'll try to address the points one by one.
1) The controls weren't too hard to figure out (wasd to move, left click to stab, is that it?) Although I did try the arrow keys first.
2) The point of the game is to gather Tissue, upgrade your light, air and weapon/tool and explore ever deeper into the depths (discovering what lurks beneath)
3) I'm not sure if it's too hard, as I don't have the time to play though without the unintentional cheating just now. But it does take a fair amount of time and effort to gather enough Tissue for the upgrades. I'm sure when music/sound is added it'll seem like less of a grind.
4) The main bug I noticed is when I press "q" it grants me the next level of oxygen tank, on pressing it again, this tank drops off and is replaced by the next grade up, after reaching the final grade it pops off entirely. The oxygen bar overflows when refilled.
I also somehow became invincible after harassing a couple of orcas that just wouldn't quit.
This was after the previous bug. I think the final amount of damage was dealt while I was on the boat, and they were jumping over and around it.
Also in relation to that the jumping behaviour. I have seen an orca jump in to the air, turn around and come back down at me, only to repeat the process.
In regards to death, when I die I can still stab, and I drift in the direction I was going at a similar speed until I hit the edge of the map. (spinning is sometimes involved)
Lastly mines don't seem to be doing me any damage when they explode, or even moving me an inch.
5) I stopped playing when after I finished the game (with invincibility) and running through a bunch of scenarios regarding orca baiting and mine hugging.
6) Changes, hmm... The word "Tissue" doesn't sit right, it seem a bit disgusting, Meat isn't much better though. A Catch Value perhaps, so that it doesn't seem like you're just handing over dollops of fresh fish guts in exchange for a new torch. Which is actually awesome... for a given value of awesome :P
The knockback from some of the aggressive sea life seems excessive at times, sometimes knocking me all the way across the map (horizontally, although a orca did manage to dump me in the deep dark)
I did find myself swimming in the air, at least as far as the animation is concerned. A "surface swimming" animation might be nice, as well as a "flying through the air after having been knocked into the sky by an enraged Orca" animation. The spinning works well, but doesn't trigger all the time.
Maybe a different scaling for animal value. When I (with great difficulty) take down a great white or orca, I'd like a payout that in some what reflects the difficulty and danger of the task. The current rewards seem low for such giant fish. I do like the low catch value of the giant Jellyfish though, real-life fisherman hatred :D
The first tank cluster
Deliberately spread out
I believe I can fly
Why can't these poor Orcas just EAT ME!
In summation, I'm in awe at how much effort this must have taken and how smoothly and well this runs. I only hope my own efforts can someday come even close.
Thankyou for sharing your creation, I hope my feedback helps