This is a level builder? Right? I've seen an engine exactly like this, four objects + player, a play and stop button, and a HUD. All you did was change the sprites. It needs work.

Okay, I have a vast amount of problems with this game unfortunately, so here's hoping this constructive criticism may help.

First of all, this page itself could use a description and possibly screenshots - presentation of the game download page will help garner interest.

Nothing in the game is explained - the purpose, the controls, what you're meant to be doing. I figure out the controls and everything but nothing else seems to make sense; there is no purpose currently. Naturally, I'm hoping you also realise that the grey block doesn't even work and both the red and green blocks have the same function, rendering one of the two pointless.
As for your character, I don't see why they have to be a block. The head inside the block would of been suffice as a character on its own.
The landing after jumping seems a bit edgy.
When playing, if you stop, you need to setup the level again as the blue blocks are gone and your character has moved/gone.

Generally, as nothing was explained and there is no purpose, the game is not at all entertaining at all. Hopefully you can make this into something.