The demos have some potential, really like the zombie one, the only crit from a technical perspective is the screen size on a few means that the page scrolls when you press space/down.
A smaller screen 640x480 / 768,480 would stop it doing the scrolling thing. Maybe instead have the controls on a quick title screen instead.
Have you tried the scroll-to behaviour yet? You can have a huge layout but have the screen follow the player, so stuff like the zombie game could be ridiculously massive, but you'd only see a small portion of the explorable area at a time. :)