I like the concept, but I didn't quite understand the game.
I played a game where the goal was to get 7. I put 2 and 5 next to each other but it didn't disappear. Maybe I needed 3 blocks? It would be good if 2 blocks would work, like 4 + 3.
Also, it's really hard to choose where to place the next block. Being able to control the blocks like in Tetris would be easier to play potentially.
For the main menu, it was odd that it needed two clicks to start the game etc. Maybe have the option (like quick start) highlighted/become bigger when the mouse is over it, instead of requiring a click, so a single click starts the game etc?