Very good course for intermediate/advanced R users. Sad that you are elegible to do assignments only if you pay.
There is much I like about this course and also many areas for improvement. First, the online book that comes with the course presents an excellent overview of the steps required to build an R package. It will eventually get you where you need to go. However, some of the material is now out of date (e.g. functions moved from one package to another), there are no longer any mentors around, and the discussions boards are empty apart from people trying to get their assignments peer graded. Also, the content in the book, while good, is incomplete in many cases. I would highly suggest buying the "R Packages" book by Hadley Wickham as an additional reference since it fills many of the gaps and goes into much greater detail.
