I think this theme has a lot of potential. I like the typography especially.
I feel that a menu icon button should open a menu, not a sidebar, especially since the same icon opens a menu on small screens. The menu icon feels inconsistent and the sidebar is more a toy than anything useful because it is not available on all screen sizes. I do like the slide down sidebar effect and wish it was consistent on all screens.
I will be disabling the sidebar and hiding the icon (on large screens) to keep things consistent on all devices.
I would also like to use the large sidebar 'header' for a book cover image. So it would be nice if the image was scaled instead of cropped at different screen sizes.