Not bad, a lot of the levels that I did were pretty good. I think I hit a couple of bugs where I managed to get the arrows to move out of sync, and to think they were adjacent when they were one square apart just by the timing of when I moved.
But level 40 as far a I'm concerned ruins the game. that level was clearly designed to MAKE THE PLAYERS HATE YOU! And I know you can't tell because of your wonky CSS choice on this page, but that was yelled in all caps. It was getting bad enough when the moving blocks came in, forcing the levels to be slowed waiting for timing even if the solution was relatively obvious, but that one really feels like "I don't have enough content, let's artificially stretch out the game." or maybe "if we make the players rage quit, we don't need to implement more levels". I'll probably never know if that's the case, because I don't expect to ever come back to complete that level.
But up until that screwy level, good job.