Before I really start I have to get some things out of the way: I don't enjoy maze games and might be biased. They are simply not my kind of game, mainly because I get bored by their simple setup. Despite this, I still think your game deserves a review, because it was rather well executed. Okay, let's see now...
You added a mute button. So your game is already superior to 95% of all maze games in existence. Good job! ;) You also spend some thought on the way the movement mechanics work, so players can not cheat their way to the goal. As far as 'true' maze games go, this might be one of the best there are. Overall, the game stands on solid feet. Quality control wise you did a lot of things right such as having a tester and fixing bugs 'before' you publish. Some of the bigger game developing studios could learn from you.
However, I also have some gripes...
Instructions: The instruction you listed in the Author Comments should also be in the game. Additionally, having "Maze Game" in the title will only tell 'most, but not everybody' what the game is about. It would still be nice if you explained the game mechanics for the inexperienced gamer.
Key Bindings: 0, 1, 2, 3 & 4 aren't really intuitive keys. How about "M" for mute/unmute, "S" (or "H") for show/hide cursor and "R" for the reset option?
Level Select: I don't think the games saves a player's progress. Skilled players 'can' finish it quickly, but a level select on the main menu would spare players that had to close the game for some reason the frustration of having to play everything all over again. Showing the current level number in a corner would help players to tell how far it is to the end and give the whole experience a more professional look. Fancy graphics may be nice, but _effort_ will always show.
'The Bug': Everybody experienced it; everybody knows about it. You added a workaround, but it would still be better for both the players and your personal experience as a developer if you could manage to find a more elegant solution.
Pride: This is only a minor thing to me, but you should show more pride. You made a game and people liked it! You should add credits to the main menu. This would as well be a good place to tell your 'story' and thank your friend that tested the game during the beta phase.
Level Design: Some levels felt unnecessarily long. Not difficult, just... more 'artificially lengthened' than actually challenging. Speaking of challenge, I noticed that the tunnel bits get reduced to 1 block width rather early on. You worked with different shapes for the most part, but some parts seem to say "I'm just a long tunnel, because the developer had some space left and didn't want the level to be over." The cannons where a good and innovative addition to the level design, but for the most part they only did the same thing, just in different places. It would have been nice if you had invested more innovation in the way you placed them. One setup that immediately comes to mind would be two cannons that alternate shooting down a 2 block hallway that the player has to pass in the direction of the cannons (with a tunnel branching off right before them). The game could also use some other 'obstacles', adding more variety.
Ending: I didn't feel satisfied when I beat the game. Sure, there's a medal, but I don't play games only for the medals, if you can believe that. A single sentence might fit the theme of the game better, but I think I would have preferred something along the lines of "You, <Playername>, are awesome!" than just a notification that the game is done now.
Story: While I can't really blame you for not coming up with a appealing back story for this kind of game, games with even the sketchiest of stories tend to be more rememberable that those without one. Throwing the hero or a princess in a dungeon is often enough to leave 'some' feeling that a player's actions inside the game world matter. And if you let a girl rescue a boy you can score points for originality as well. (Which is still something that is hard for me to wrap my head around: The dark ages are long gone, but still most protagonists in gaming are dudes... What is wrong with you, world?)
Still... All in all you did a pretty good job. It's just that I think some tweaks might have made it 'exceptional'.