I would like to receive comments on my website, a digital textbook on probability theory and statistics.
In particular, I would like to know whether:

- there are obvious flaws in the design of the homepage and of the inner pages (things that feel out of place, inappropriate use of colors, fonts and other design elements);
- there are usability problems;
- there are things that could be improved SEOwise;

Also, if anybody is an expert is statistics, comments on the content would be highly appreciated.

The website is at http://www.statlect.com