I'm thinking about renaming the game to "Emo-Sokoban" :-)
Your problems are shared so many others, I think I should double-think in case I want to make another isometric game. I was inspired by the Mini Quests
I've had lots and lots of complaints about the controls in that game as well.
I think that Cas's comment in that thread may be on target: if you can make the game be controlled by the mouse (and I'm not sure how you would in this case), then that's the way to go.
One aspect of the controls that you could improve though is the way the keys auto-repeat (on my keyboard at least). If you hold a key down slightly too long, the character zooms off into the lava, which makes the game a little more tense than you probably intended.
I did like the narrative aspect of the game (the intro and the ending). A couple more 'narrative bits' partway through the game might have been interesting.
As philfrei said, showing a level number would be good. In particular, if it said something like "Level 7 of 10" then that would let people see that the goal is within reach. If the comments in this thread hadn't mentioned the game's ending, I probably would've assumed that it just got more and more difficult, and might've given up without seeing the end.