All you said was noted, but I'd like to reply to the graphics issue!
I actually didn't notice that before you pointed it out. I had actually made sure that all the sprites are created in 16x16, even though the game scales them up to 48x48 to make the edges appear more clearer...
Now, I guess the issue is not the pixel size, but the fact that I've createt the wall and floorpieces, to look kinda realistic and I used gradients and more dynamic shading than on the player sprites.
This is definitely something I will have to improve in future games as I really didn't notice that! Thanks for pointing it out.