Nice attempt. But it needs a lot of things to make it playable.
First, and this is the easiest thing to fix, allow the player to get past the continue button with the keyboard instead of just the mouse. If you don't do this, the keyboard controls in the rest of the game are for nothing.
Second, you gotta make the isometry less ambiguous. Maybe have a color code so you can tell what height a block is at. And make everything transparent so blocks can't block other blocks.
On level 12, I glitched into a wall by going down through a portal when the exit portal was right on top of a wall. I could move out of the wall, but strangely enough I could move right back into it.