This was a surprisingly fun and addictive game. As something of a rogue-like purist, I was worried about the "Rogue-like + Puzzle" description. However, I feel it pulled it off quite successfully. In fact, I enjoyed it so much, I will make a point to bookmark this page so that the next time I have the extra cash to do so I can remember to buy this game.
As it is, I feel the game is VERY nearly perfect, but only with a couple of minor flaws that I feel could be easily corrected. First and foremost, I would really love to see a one-step undo button, which will undo the very last step you took. I feel this would benefit everyone, as it is easy to accidentally spend a key or get into a fight that you didn't mean to start with a very minor misclick or press. This can take a well-to-do play through and turn it into a rage quit in as short a time as it takes to accidentally attack an "infinite" monster and lose over half your health before you realize what just happened.
Secondly, I feel there should be some clue as to the nature of each boss. I very nearly died to the third boss by not being able to factor in the fact that the other creatures in the room get to attack first. If I hadn't had the foresight to scum up my attack to 150+ to one-shot the lizardmen, I would have been killed right there. Perhaps the Elder of each level could clue you in to the way the boss fights. The first Elder could suggest you bring a bomb, "just in case" you get surrounded. The second could refer to the 2nd boss as "an unholy monstrosity," or something like that. The third could tell you the Dwarf Captain's leadership is making the monsters under his command more agile. Make the clues more subtle as you progress, but there for a keen observer to pick-up on.
Third, I don't understand the value of the crystal ball. Even if you aren't sure if it is worth spending an extra key to get an upgrade now, you can easily take the safe road and open the way to the stairs in order to take a peek. I guess it works okay in conjunction with the floor skipping scroll, but if someone is actually considering using one of those they probably are stuck, meaning exactly what is on the next floor isn't all that important to them since whatever is up there can't be any worse than being stuck as they are. It really seems to be a widget item; fun to play with but has no purpose. Perhaps it can be changed to function as the one-step undo I mentioned? Or perhaps as an upgrade to that feature?