Many of the works of Dickens can be a bit laborious to go through, simply because of their size. That alone tends to put a lot of people off of reading them. Many are wanting faster books, or quick reads, as the time to sit and concentrate on a book is not always easy to find. However, once one begins to read the novels, they are not difficult to understand, when taken for pleasure reading. They are recommended more for high school ages and up, given that some of the terms used in the books would be over the heads of those who are younger.
The challenging aspect comes in when one begins to break down the books and look for the deeper meanings in the text. If you take the book at face value, they are fun and delightful classics. When you begin to flesh out the different aspects, therein lies the harder aspect of reading Dickens. The many social issues that he tackled through his writings are laced through, and one has to really dig deep into the wording to figure out the deeper meanings. If one were looking for a great classic, then Dickens would be the go-to choice. However, if one is looking for a book to use for term papers or discussion in a literature or history course, then again, Dickens would be a perfect choice.