Im learning actionscript myself now and what you made here is something that someone like me can make with about 3 months of actionscript experience.
but simplicity does not have to be a problem for a game (look at pong it is still popular) but with a few changes this game can be much more fun.
so here is some advice:
1) the block you used as a character is a huge mistake. it looks retarded and the changing of the sqaure was anoying and distracting. next time use a normal square or a real character.
2) the game had only the black walls and the red triangles to make you die.
you could make lots of stuff that makes the game more interesting like floor that turns into a wall after you pass it (Im not gonna explain it in detail but basicly you have to make the floor detect when the player is on and as soon as the player no longer interacts with the floor make a child (of a regular wall) at the location of the floor and after that destroy the floor (remove child).
3) try to make a ending to a game instead of trying to anoy the player when he reaches the last level.
4) practice a lot
5) ask someone with more programming experience to look at your work before posting it. he or she might help you to point out some stuff that doenst feel good and might give you the propper code solution
good luck with future games and keep it up.