I have been progressing through all the courses in this specialization and, overall, the courses have been of tremendous value to me. However, it's really not the courses themselves but the book that goes along with the courses that deserves the four and five star ratings I have previously given (these courses are really nothing more than "read the book" and "take the assignments"). Nevertheless, the knowledge gained is not easily available elsewhere. 80% of this visualization course (i.e. the book) was excellent and I give it top marks. The other 20%, starting with the grid system section to the end of the book, was terrible. These sections need a complete rewrite as they are barely comprehensible and certainly not comprehensive. The final assignment does not test you on how much you learned in the course, rather it tests you on how much time you spend on your own finding other relevant sources of information on the internet to figure it out. Also, I don't understand why creating a custom geom would be a more important software development skill than R Shiny for example, given that having the ability to develop interactive apps is critical to visualization. I will give this course 3 1/2 stars, rounded down to 3 since coursera won't allow a half star. I hope the authors take what I have to say as an opportunity for improvement since I have benefited tremendously from this specialization so far and I would like to see it improved in certain areas.
