The animations are choppy to a distracting level on Chrome 22 running on a reasonably beefy desktop machine.
The font size is unreadably small, and due to the three column layout it doesn't degrade well when zoomed. It'd be merely crappy if zooming required vertical scrolling. It's disabling all methods of vertical scrolling entirely that really make this design special.
It replaces normal page navigation with a custom version, which is already bad. They then compound that error by mapping that custom navigation to the wrong keys. An example: maybe you'd like to check one of the footnotes they have. In a sensible design those would be hyperlinks, but for whatever reason that wasn't done. Ok, so I guess you need to go to the end of the document to see the footnotes. Wouldn't still be too bad, but they forgot to map the "End" key. So the only way to get to the end of the document is with the slider. And after doing that, how do you return to the original position? Well, I'd expect to be able to do Alt-Left for that. Except that this keybinding has been overridden too, and you need to instead click on the back button.
Doing this kind of stuff might be just about acceptable in a web app. But this isn't an app. It's a document. And they've managed to break the only two things that matter for a document. I need to be able to read it, and I need to be able to navigate it.