I've read a lot of Shakespeare, in school and out, and all the Harry Potter, Lord of the Rings and other Tolkien works, but I couldn't force myself past the first few pages of Twilight. I skimmed ahead a few chapters, but it looked pretty horrible all the way through, and given that pretty much everyone whose literary opinion I in any way trust told me it was horseshit, I didn't care to find out personally.
Shakespeare was a literary genius. Even if you don't like his material, you have to give credit where credit is due; he invented many, many words in the English language, his wordplay was witty, funny, and very beautiful. It's hard to read, because we don't speak that sort of language these days. (NOTE: It is NOT Old English which he wrote in. That is a separate language entirely, with, I believe, an entirely separate alphabet. My favorite English teacher taught us that in Freshman year, telling us that if she caught us referring to Shakespeare as "Old English," she would make us write our essays in -real- Old English, and we would probably cry. Or something like that.) I got lucky in that my parents raised me on the Old King James, which is written in very similar language; I get the dirty jokes, and the metaphors, pretty easily, because the language isn't as much of a barrier. But, no matter whether you -like- his style or not, he was a literary genius. (Did you know that "nothing" referred to a woman's... yeah... back then? When I learned that, it gave a lot of his lines sudden new, hilarious meanings.)
As for the "LotR craze," no, it isn't dying down. The movie craze is. But the books? Were written... circa 1954, 1955. That's about fifty-five to fifty-four years of popularity. When a student teacher saw me reading The Silmarillion in History, he remarked that they seem to come back with a bang every twenty, thirty years or so, since they'd been fairly popular in the fifties (I think), huge in the eighties, died back down a bit, and then became huge a few years back, when the movies were made. Twenty-five years or so from now, people will suddenly rediscover them, I'm sure if the world hasn't ended by then. It's not a passing craze. Tolkien was also a genius, in his own right. (As was Lewis, given that The Chronicles of Narnia also come rushing back fairly often.)
Harry Potter? Who knows? I think it'll be something along the same lines, though personally I prefer Lord of the Rings, Narnia, or, in fact, Shakespeare. HP is good, though, very good, and, as you pointed out, it's now a part of culture. Also not a passing craze.
Twilight? A passing craze. In twenty, thirty years, people who read Twilight and Eragon might remember them, might still enjoy them, but they won't be huge things like LotR and Shakespeare and possibly Harry Potter will.
The comparison thing isn't that ridiculous, as far as who stands the test of time. Honestly, it's not that ridiculous as far as quality is concerned either. Somewhat ridiculous, yes, because Shakespeare was a playwright, not an author, and because he wrote at a point when language was changin drastically (though, I suppose, given the sudden veer we've taken towards babble like "Obvy, FML," and oh my God I can't think of any right now but I meant the craze of abbreviating every single word, even in conversation, you could consider this language in a transition phase as well), but all told, I think he still wins on sheer awesome. His sonnets are awesome. But Stephanie Meyer? Oh good grief no. Her writing is purple prose, and at best, angsty melodrama. (Shakespeare, by the way, also gave us realistic acting. Back then, acting was nearly always incredibly melodramatic, the sort of thing you'd see in a bad soap opera today. Shakespeare was the one who started the whole thing with acting like real people onstage.) JK Rowling wrote well, if not as well as Tolkien, and Tolkien wrote well, and invented NEW LANGUAGES AND AN ENTIRE WORLD COMPLETE WITH FULL GEOGRAPHY HISTORY AND MYTHOS AND BASICALLY INVENTED TODAY'S FANTASY GENRE, but Stephanie Meyer? Wrote a story which ignored all previous vampire lore, a story in which the main character was a whiny brat and the other main character was an abusive jerk. And, because the characters were described in urple prose as the ultimate hot, tween fangirls ate it up. And some other people. But you know how you see those fanfics that are just horrible, horrible stuff, and somehow they have thousands of reviews of "ZOMG I LUVV U THIS ROXORZ" and, more mind-bogglingly, here and there, well-written reviews that actually point out good things? That's like Twilight, in my mind. Yeah, she got published, and she's got a thousand fangirls who fawn over her and are prepared to flame (and call a flamer) anyone who doesn't. But at the end of the day, give me Don't Panic, Okay NOW Panic, any day of the week. And if you don't know what those fics are, and you have ever typed "Where is all the goodfic?" then slap yourself upside the head for me, and then go read them. Please.
(Rambling is a key trait. Nourish it well. :D)