Before I say anything else, Bombfiglio, know that I favorited this game and have given it the rating I have because I see potential in it.
This game has a wonderful concept--easily professional-standard. The plot is simplistic, but it doesn't need to be complicated for something like this. The aesthetic appeal is limited, but with what you had to work with, you've done a marvelous job. The idea behind the steam-sword and its function is marvelous. I could see this swiftly taking the gaming world by storm if handled by a professional game studio.
BUT.
You've posted it far too soon. I would recommend taking what you have and going to a flash game group to have the look and definitely the control updated. There is nothing wrong with this game, sir. It is a gem. It simply needs more polish.

Every time I attack it moves my character left.

I voted a 5 cause this my bro right here

Bad on all fronts. Aesthetically, the game is unpleasant. The art style is interesting, but there's too much brown, and it can be unclear what's an enemy. The stomping hand thing, for example, is brown like the background, and doesn't immediately stand out as dangerous until it actually attacks.

The 3C's are particularly bad, and what really breaks the game.

The player character is too big, either that or the camera needs to be zoomed out. Giving the player a better field-of-view would greatly help in both combat and platforming. With the way it is now, I jump, and I have no idea what I'll be hitting my head on.

The attack animations cut off the moment the player lets go of the space button. Meaning I don't know if the attack registered on the enemy. Add to the fact that there's no hit indication, no recovery time (enemy comes near you, and you just start bleeding), and this awkward sword swing that requires timing, the combat is terrible.

The controls are a mess. Why are there so different buttons for regular movement, and the "steam" power? Why can't I just, say, hold down shift, and then move to activate steam?

This game is unacceptably buggy too. My character seems to bounce randomly without reason. Every time I click on an in-game menu, I lose functionality in the game. I have to click on it again to regain control. I've never seen a flash game have that issue before. On the first play-through, I fought a boss at the start of the game. He killed me, and I started again. On the second encounter, he died in one hit. I think his health status somehow rolled over to my second game. But what's weirder, is that on my third attempt to play this game, I didn't even fight him at all. I guess it was because he was already dead?

Can't honestly say I felt like a "thief" in this game. I felt like Dante from Devil May Cry. Granted, I didn't get far, due to the issues above, but I couldn't grasp where the thief angle came from. Will I end up actually trying to thieve some stuff in this game?

Get some quality control in this game. It just isn't playable in this state. Could be cool once it works properly, but it's nowhere near that state right now.

The movement is choppy, object collision isn't very well done, and the animations for the "sword" look like you're swinging a broom.