I liked the monsters but you could improve them quite a bit. add some color and maybe some particle effects coming off of them (like in alan wake, I realize this is a flash game but just the idea of the smokey effect). The beginning of the level is so random. you just float up onto the platform from below. you could have a short cutscene of the guy falling onto his face and then getting up and being chased by a monster. Before I finish and get thumbed down for criticizing the art I just want you to know that the animations were great and I loved the floating squid-things in the background.
I would like to touch on the art. I don't hate the graphics but the title of the game is "Nightmare Runner", I think that the game should be darker. Keep in mind though black isn't always darker. I mean darker as in grainier, more rough. Also, yellow for a background was poor choice in my opinion. In my nightmares the sky is usually either pitch black or dark red. I realize that you tried to make it look very alien but I think it just looks wierd.
IMPORTANT!!!!! There is no save button and the game does not autosave. I lost all my data when I closed out of the window. The game ONLY SAVES WHEN you click exit game. + so people do not lose their data!!!