This is super cool! I really, really enjoyed the twist and getting one ending made me really want to replay to see if I could get a different ending. (I got very very bad ending!!) There was good foreshadowing for the twist, too-- the first time I felt like something was wrong was whenever I stepped in the sludge and sunk in, and then I was really hooked to keep playing. The enemy designs were super super cool and I loved especially the last boss of the dungeon. I really loved getting to play as the hero of light and feeling super overpowered, then getting to the ... enemies near the dungeon entrance (trying not to spoil it)... and getting beaten so easily.
I think that some of the game is lacking contrast and some things are hard to see, and the camera swinging around during battles was pretty tough on the eyes. I did however love all the animations in the game (the dog getting hurt and his eyes going wide was so awesome and made me really feel the hits!!) and the characters are pretty classic. I love that there's a dog!
I didn't get any use out of the upgrade mechanic as once I went into the dungeon I never left until the end. Maybe the scaling could be a bit more difficult so that you feel like you have to go upgrade your weapon?