I have some feedbak, nothing major, but I would say that a professional designer could help you improve the book cover. Right now somebody with professional experience in graphic design --or a good eye for design-- can probably see details in it that could be improved. It's a pity if you have worked on this for five years, not to present it in the best possible way.
The cover design is nice enough IMO, but it definitely looks like a self-help book or something rather than a technical monograph.
The image on the site has incorrect capitalization ("A History of..."), though the one on Amazon appears to be corrected.
It's more likely that they focused on the book's content rather than the cover art for 5 years
Yup. I'm not happy with the design. Some promised assistance fell through and so I had to scramble last minute. I've seen worse though :)
(Specific tips on improving the current design welcome, most stores allow edits)