Ooh, this is a great thread! I've been waiting to unburden my load
First,
The DaVinci Code and
Angels and Demons by Dan Brown. I got TDVC to read on a plane (nothing better available), and it was 'pretty good' apart from the horrid, stilted dialogue and the incessant grammatical errors... but the ending sucked badly. Dear MrCoffee went to England and got me Angels and Demons (to get a 3-for-the-price-of-2 book discount) and it was so bad I felt like I was bipolar: 'oh-my-god can it get worse? vs. 'oh-my-god this cannot possibly get worse', and battling over whether I should drop it lest it get any worse, or whether I should keep going to see just how bad it can get. In that sense it wasn't a disappointment, because the ending was so bad I doubt anybody's ever managed to publish a book with a worse ending.
Then,
Lolita by Nabokov. FFS, we all know just how intelligent you are. All the literary references thrown in so that you can laugh at your stupid readers who don't 'get it' get tiring. I swear, he wrote the book just so that he could feel superior.
Oh, here's a bad one:
Lost in Translation by Ewa something-or-other. Must confess, bought it because I thought it was the novel that the movie was based on... haven't seen the movie but it did seem interesting. Well, this book shares a title with the movie, and that's it. And it's written in PRESENT TENSE. Horror of horrors. 200+ pages of "I'm four and walking down the street and after dinner I ask mama whether she blablabla". There are tenses in the English language for a reason.
ANYTHING by
Ruth Prawer Jhabwala (sp?). As a fan of Anglo-Indian literature, I picked up a couple of her books. Bad mistake. I really had to force myself to finish them. What's wrong with them? Many things. For instance, I was almost through one book when it turns out the main character/narrator is a 17-year-old lesbian. Now, throughout the book she comes across as a prude in her mid-30s. THAT's BAD WRITING. Not to mention the lack of editing...
I could probably go on (I don't think I've ever left a book I've started unfinished--gotta get through them even if they're bad; I always give the author a chance to redeem him/herself, even if it happens in the last sentence!) but maybe I shouldn't burden you guys with a longer list.