I think the thing with Twilight and Harry Potter is, largely, you're supposed to be drawn into a different world. I really like Harry Potter, but I think JK Rowling is a terrible author. The last book was the most well written book, and there's still a lot about it that I think she could have done SO much better with. I think the Twilight books are terribly written too - BUT it's more about suspending that and getting into the WORLD... the story, the adventure that's going on in the world. Not really how well written they are LOL. I did not like the HP books for a long time. It wasn't until after book 6 came out that I decided "fine, I will give it another shot." It took me like, three days to get past the first few chapters of Book 1 because it was SO BAD. But then I got past this threshold where suddenly I was more interested in the WORLD and the story... and I read the rest of the book in a day. Books 2 and 3 took me a day each after that (then book 4 took me a week because that is the slowest freakin' read in the series.) It was like, okay, once I got past the terrible writing and actually fell into this world she created, THEN it was interesting and exciting. Not like it's the most original story ever, but I'm not the kind of person who insists on stunning originality or I just can't enjoy something.
Personally, I find Bella to be the most irritating character in the world, and Edward is obnoxious too, so I haven't been able to even get immersed in the story since I can't stand the two biggest characters, LOL. I spent most of my time reading the first book and whatever I made it through in the second with an overwhelming urge to smack both of them. As for the movies, I honestly don't think Rob Pattinson can act very well either - he was very awkward and stilted as Cedric Diggory in HP4, so I cannot imagine WHY anybody would cast him ever again, let alone as the lead male role! (Also dear God can he just brush his hair and stop looking like such a douchebag? He was SO much more attractive as Cedric.) So with Kristen Stewart doing a crappy job and Pattinson screwing it up opposite her, it makes the movies painful for me to watch.. Taylor Lautner is totally the best part about the movies, LOL. I'm not even on Team Jacob, I'm just saying. *whistles*
It reminds me of Star Wars: Episode 1-3. George Lucas did such a smashing job making fine actors like Liam Neeson and Ewan McGregor deliver stiff performances. =P It's that same level of painful to watch. But at least you can still immerse yourself in that world and enjoy it for being Star Wars rather than "wow, this is the finest piece of cinema I have ever seen!!" So I think a lot of people can get past the things that I can't get past and still enjoy Twilight because it's an interesting world she's created. Again, not the most original, but still interesting.
Not everybody that likes Twilight is an annoying teen... a lot of people my age and even older enjoy it. Not for me, but they like it, and that's cool by me. I think it's actually kind of cute sometimes, LOL. One girl is 22 and she totally bought the Bella bedding set for her bedroom. That's my kind of dorkiness. <3