Nicholas Sparks' books are what I call "dessert" reads. (Not "desert" as I would prefer to have actual literature with me in a desert!) They're harmless, but contain no actual value for the mind. Too many of them, and the mind becomes sluggish and it becomes difficult to think critically about "meatier" books. It's important to have a balanced literary diet, just as it is important to have a balanced nutritional diet. Pop fiction (Sparks and other formula writers like him) is fine now and then, but real growth in intellect, rationale, and philosophy in found when true literature forms the base of the library.
Unfortunately, I believe his books are rather formulaic. I think that Sparks might like to think of himself as going against the grain because of his numerous unhappy endings (Dear John, Message in a Bottle, Nights in Rodanthe, etc.), but to be honest, most people have come to expect an unsatisfactory ending from him. While most readers will accept a realistic ending (not necessarily a happy one), they do so because the author's writing is powerful and moving, and the ending fits (i.e., The Great Gatsby or Of Mice and Men). But Sparks seems to tack on rather depressing endings to categorize himself with classical writers when he does not demonstrate the same skill as those writers (at least it's not demonstrated in any of the books I've read by him).
Many of my female students love reading Sparks' books, and I'm glad that they are enjoying a book, but I would rather they read someone such as Jodi Picoult whose rich writing is not only more enjoyable than Sparks' but who also gives my students a style that they would do well to emulate.
I think of Nicholas Sparks books as light, beach type reading, and while I think it's better than not reading at all, I don't think it's especially stimulating to one's intellectual growth. His books tend to be love stories hinging on the melodramatic, with very similar plots and formulas. The plots and resolutions tend to be very predictable, and well-suited to a "movie of the week" type adaptation. In other words, there's nothing wrong with these books, but I don't know that they qualify as literature because they don't really stretch our minds or cause us to think very deeply about the human experience.
Nicolas Sparks is not literature. It's light reading, sometimes fun plots, but a very quick read. I read The Notebook after people raved about it, but found it to be very trite, and underestimating of my intelligence. In other words, I figured out the "twist" very early on (it's very obvious). However, his books translate into decent movies, in one of those rare instances where the movie is actually better than the book.
They are okay, not great. Young adult girls like them a lot because of the romance in them. But after a few they become predictable.
I haven't read the novels you mention, but I recently read Nights in Rodanthe and was very disappointed. There were numerous instances of plot summary that bothered me as a reader. Instead of developing a scene, Sparks summarized the scene by simply telling what the characters did and what they said to each other. This kind of writing cut out much of the narrative, leaving the novel very thin indeed.
Some of the books lack concrete description that is needed to develop an exposition. The books could use much more depth, but, if you area follower of that reading style, then many people will enjoy the stories. If you need more depth and deeper ideas, then you should look elsewhere.
sorry to say this but not great
some of his books like notebook, walk to remember as well as message in a bottle r really nice.