I'll meet you half way - Potter perhaps doesn't dip into the murky literary ether that is the Twilight saga. But, it's not what I would call "great literature" either. Is it entertaining? My kids, all of whom read the books, promise me that it was. However, Is Rowling this generation's Cervantes? I'm thinking no.
Rowling is not the best writer, she may be this generations Cervantes, considering how limited this generation is.
What makes literature great? Is it how well it is written, how timeless the story is, how well a particular generation regards it?
I think the Potter books will be last. I don’t think she will replace Tolstoy or Dickens in terms of how future generations regard literature, but she has made a mark.
Twilight, however, really does suck.
Not, perhaps, "great literature" on the level of, say, Tolstoy -- but Rowling was not writing for adults. (Although this adult greatly enjoys the books, to the point of having re-read them.)
She does, however, succeed in several very important ways.
First, she is among the best authors I've ever come across, in her ability to create a scene with just a few words. One can comfortably "move around" in her world, because one can imagine it in very good detail. That's a big part of her appeal, but not the only thing.
Second, she deals with Large Questions in ways that make the reader think. The books deal with the rise of evil in a society, and the characters respond to that in various ways (realistically). None of the characters is perfect (which is good); but they carry on even as the going gets difficult. (I think Rowling drew a lot of her story line from 1930's Britain...)
And, although she's not blatant about it, she is a Christian, and her theme is essentially Christian as well. In an interview several years ago, she hinted that anyone who knows the Bible, knows how the story will turn out. And a discerning reader has absolutely no difficulty in seeing her what she means by that.
Finally, you care about her characters: you like the ones you're supposed to like; dislike the ones you should; and there are the ones who surprise you, for reasons that matter.
So as young people's literature goes, I think the Potter series will endure for quite a while. They'd be on the same level as Narnia, Oz, and perhaps a few others.
And as for you .... you might try them out. They're a lot of fun.