I loved LOTR and Potter and have always been a Sci-Fi/Fantasy fan. Narnia (movie) pales in comparison but that may be because it was targeted to younger audience.
Have you ever looked at the stories that you are comparing.
The LOTR books have over 1000 pages.each.
The Harry Potter books have over 700 pages each.
The Chronicles of Narnia have less than 150 pages each. They are made for 8 & 9 year olds to read.
You cannot get that much information out of a book that is less thank 150 pages.