Unsurprisingly enough, it contains some options that you might want to change before entering the game. Specifically, it has options for video resolution, video effect quality, and sound. For the most part, these are the same options currently available in-game. "Enable Reverb," "Headphone Mode," and "Death Knight Voices" have been added to the sound pane. "Disable Resize" has been added under "Windowed Mode" in the resolution pane; I'm not sure why you'd want to do that, though, unless you kept accidentally resizing the window (which I've never had an issue with, and I often play windowed).
The big innovation here (and yes, I realize innovations in option dialogs may not strike you as particularly interesting) is a master slider for video quality. Now you don't have to fiddle separately with terrain distance and ground clutter density if you don't want to; just drag the slider somewhere on the scale from "Low" to "High," whatever's prettiest without being too devastating to your framerates on your particular system. Of course, there's a "Custom" setting, so if you want to tweak all the little sliders, you are still free to do so. A nice change, and it will especially benefit people who don't necessarily know what all the options mean.
Gallery: New Options frame