As for actual advantages and features, I was thinking of incorporating that into the "what is Sphere?" bit.
Looking at the page again on the desktop, I don't like the positioning of the screenshot box. It takes up half of my 1080p monitor and sits above the "What is Sphere?" section, which I have to scroll down to actually read. I'd recommend reorganizing it a bit to make the introduction readable without scrolling, so that newcomers can find out exactly what this thing is that they've just stumbled upon; the slideshow should go alongside the intro text as if to say "See? This is what you can make with our engine!".
But actually, my plan was to have two columns for the "what is Sphere?" bit: really clear, succinct text on the left, and... a screenshot of Sphere in action on the right. But now that I think about it, that screenshot could totally be just the game preview slider.
Also, "XMLHttpRequest". For a class that has nothing to do with XML.
Well, yeah, I wasn't faulting you for writing the code (or copying it, as the case may be); it just struck me as lazy API design. Also, "XMLHttpRequest". For a class that has nothing to do with XML. I think whoever designed it must have been on crack.
Anyway, I did notice you seemed to be hung up on the page content. Unfortunately I don't really have any suggestions... this is why I never made a website for miniSphere.
The "latest miniSphere version" thing doesn't seem to work though?