I think geographical, chronological, historical and technical aspects need to be correct, or have an author's note to explain why they were changed.
There should never be spelling or grammatical errors unless they are in direct speech and add to the character. However, I do read a lot of uncorrected proofs, and so have to be forgiving in those cases (and just hope they get picked up before publication).
However, it doesn't have to be great literature. I quite like an escapist read, and I don't like to have to reread a sentence because it is so complicated I couldn't get it the first time around.

Astrokath, AMEN!!!!!

Me, too. Many years ago our public library took The Bobbsey Twins out of circulation saying they were not good enough to carry. I do realize they were not good literature, but they were fun for children to read. Escapism is good enough for me!

I'd agree with Astrokath. The mechanics of using the language do have to be right in a novel. (Don't worry, posting on the internet is different.) The plot should make sense and internal logic of the book's world should be consistent. The author can't change the rules in the middle of the game because they become inconvenient. If the author decides to change historical fact, okay, but it should be acknowledged, not presented as if it were truth.

But I am perfectly happy to settle for entertainment rather than enlightenment.

Rosefolly

Perfect? I don't know if I've ever read a perfect book. Probably not. I'll forgive the writer for a multitude of flaws as long as I like what I'm reading.

I'm all for entertainment. If I get a little enlightenment along with it, so much the better!

Depends upon my mood.

I picked up a romance novel off the top of the pile earlier today at Baby Sis's. The cover described the cowboy hero as retired FBI; the first page described the cowboy hero as retired CIA.

Doesn't have to be perfect, but I cannot abide books that are entirely predictable.

I would say that there are times when a predictable book, well done, can be a comfort read. I suspect that is why series books are so popular.

Rosefolly

Well put Kath. It should be up to the sub-editors of publishing houses to correct the spelling/grammar of their authors, although I have started more than a few shoddily written books that have got under the radar. I can also put up with a few liberties in a historical context . . . but not to the extent that 'Hollywood' often alters facts so as to leave a susceptible audience being taken in by some total fabrication of real events

I can overlook a lot of things--typos, alterations in geography and history so long as they make sense in the context--if a story is well-told and captivating. I do want to be transported. I want magic--without sentimentality or cheap tricks or sensationalism. A typo here or there doesn't bother me (and I'm an editor).