Great Game!
I thoroughly enjoyed playing this game, however I think two things would benefit this game:
1.) The ability to create blocks en masse.
The advantage of this is being able to hold down the mouse button and drag the cursor across the screen to create blocks wherever your cursor goes. I'm sure you know what I mean. You wouldn't need to click for every single block to appear in a long wall of blocks.
2.) The ability to chat with others.
I loved playing with other people and I think the online aspect was brilliant (as it is the core of the game), however no online game is complete without a chat feature. If I were to create any online game, I would immediately incorporate that. I sadly resorted to using blocks to spell out things, but that was very impractical and any communication was severely limited.
Other than those two critical features, this game was a pleasure to play. I give you a 7/10.