Boring!
The physics are really good, but there are several things that need a lot of improving:
-The english is pretty terrible sometimes. Why don't you have someone who actually speaks english as their first language to review your text?
-Climbing and dismounting stairs is annoying and difficult.
-Gordon should be able to run faster than he currently can. Slow pace of game = boredom
-Give Gordon a GUN to start off with and more enemies to fight! It is really boring at the beginning of the game running along the screen (very slowly) and having nothing to shoot or interact with.
As I said, you've done a great job with the physics code, and the graphics are nice. But the gameplay needs to be improved dramatically for there to be any fun!
2/5