Twilight WAS bad. Even Stephen King said it was bad. He was quoted as telling Stephanie Meyer she was no J.K. Rowling. When one of the most famous authors of our time disses it? Then you know it's bad.
As for why it's bad...
My biggest pet peeve was ...
#1. They take 300 pages and half the book to bring out that they're vampires. That long to find out. YET on the back of the book (the back flap summary) right there! It admits plain as day they're vampires. Tells you, doesn't leave any surprise. If you're going to take that damn long to reveal some high plot point, don't give it away on the back cover. The part that EVERYONE reads before even buying a book. That's just stupid. It's not suspense if you already know what to expect.
#2. There. Is. No. Plot. The whole book is Bella's school life day by day, a little bit different each day, with her just complaining and talking about Edward. Ever read those old books the Sweet Valley High series? Or Soap Operas? Hell, even a Soap Opera has a plot. This doesn't. The whole first half is you just reading her every day life. Any writer knows you have to have conflict and and a point of action after your introductory. Twilight doe snot. The whole thing is introductory with some action thrown at the end as a conclusion. No climax, no point of action, NOTHING TO KEEP YOU READING FOR. It does not draw the reader whatsoever.
#3. Bella is a Mary Sue. She's too perfect. She has now flaws. She has nothing that would make Edward fall for her, and yet he does (out of nowhere just the whole "love at first sight" deal.) She faints at blood. Oh dear me! You're surrounded by vampires and the best flaw you can give us readers is to faint at the sight of blood. -.- The love scene happened way too fast with nothing to even bring the characters together.
#4. Adding to #3, Edward falls in love with Bella THE DAY SHE GETS THERE. He ignores and gets mad at her because he was in love with her. She did nothing to make him fall in love with her. Did nothing out of the ordinary and wasn't even described as all that pretty. He just fell in love with her and watches her sleep/stalks her to her house. Just because Stephanie Meyer threw in LOVE AT FIGHT SIGHT. Yuck.
And.. #5. As a friend of mine said, "The whole book was just a way to describe how drop dead sexy Edward was with a little story thrown on the side to make it a book." It basically is. For every noun Stephanie Meyers threw in 6-8 adjectives. She completely overused and abused the Thesaurus and brought in words that would make you have to have a dictionary by your side just to give more information on how beautiful Edward was. When by all rights the way she described him, he should be a homosexual. Any writing book will tell you to go easy on big words and using the thesaurus to give more than one word for the same thing. Oh and they also warn to not repeat yourself to the reader. Meyers does it all.
...And that's not even going into the whole Sparkles in Sunlight and destroying Vampire Lore. That's just about the writing its self. For the Lore.. Vampires in love is okay if done right. I mean I loved Anne Rice's novels. Lestat forever! But... she knows how to write. Meyers does not.
I only read the first book, so I can't tell you how badly done the others were.