Very cool and brutal
This is very well animated, and it seems you've put a lot of effort in it.
GOOD STUFF:
The idea isn't new, but who cares, it looks pretty good. Especially the blood looks awesome, and the droplets of blood spraying add to the violence.
Backgrounds look good, you've used light and shadow as contrasts a lot, which works well, since it's in an asylum. Also, the color-theme is very gray except for the blood. This makes it more "cold" but also makes you concentrate on the blood more. So it seems like a well conducted blood bath.
THINGS TO THINK ABOUT:
Visually the main character didn't differ from the guards, which allows for some confusion. Also, the screen blinks too much IMO, and adds to the confusion.
It's pretty long. Although well done, I started to get a bit tired of the same song. Might be a question of taste, but I would've enjoyed hearing more than one song during the flash.
It could have some background story, but maybe it didn't need any. That could've just seemed forced if applied...
Good flash, keep it up.