I really like the flags and blocks, they're a neat way to introduce interactability in mazing.  Also the trees surrounding the outermost edge are a nice subtle touch to get your bearings.  The way the character turns automatically when colliding with things was a bit frustrating though, I woulda loved to have mouse look but I understand thats not possible with 2 person controlling on the same machine (I didn't have someone to play with though).  I did find a bug where I placed a flag inside a wall accidentally and when I tried to pick it up the player got locked in place trying to reach it so I lost all control.  Oh and the main menu looked great!