I read an article the other day on writers who were hugely popular and are now languishing in the also-rans: DH Lawrence and Hardy were cited as forgotten titans. That struck a chord with me: I devoured Lawrence as a teenager (no, not just for the dirty bits: they're couched in such overwrought terms that the effort isn't worth it if you're just after some filth) but found recently that I couldn't get on with the novels - though the short stories and poems really stand up. Ditto Hardy, of whom I'm a fan. Lots of people have said that they can't stand them - but I have a taste for melodrama and rural folk (hence The Archers) and happily get through 800 pages of child suicide ('because we are too menny'). That said, I'm now convinced that Hardy's poetry is much more significant than the novels.
Who else? I can't stand Tolkien anymore (despite Ben's claim, which he printed on a business card, that JRR Tolkien is blocking my cock). I read the lot when I was 14-15, untold kilos of biblically-cadenced sons-of-sons-of Beorn the bloody bear: now the clunky prose, awful dialogue and terrible characterisation stop me about 5 pages in. Except for The Hobbit, which is light-hearted enough to win safe passage. There must be loads of stuff I read as a teen and would now reject. The Thomas Covenant and Amtrak Wars series - why? Ann McCaffrey's Dragonriders of Pern fantasy series. I've also largely given up on Delillo, Auster and McEwan, having spent 15 years loving their back catalogues and being progressively more disappointed or angry (that's you, McEwan) with their new stuff.
Other books I'm warming too: I used to have a blanket ban on Dickens, but I'll read the darker ones now - nothing that tries to be funny, mind. Ned Cheeryble should be stabbed in the kidneys. I'm trying Milan Kundera again - at 17 I thought that The Unbearable Lightness of Being should be The Unreadable Dullness of Pretension, but I'm slowly coming round.
So what are the books you once loved and now can't stand?