Personally, I rather like well-written AUs. But I have a thing about no OOC-ness. That completely turns me off whatever I'm reading. So I tend to be picky about what I read and write.
Well. I suppose I should say that I won't write it if I can't see myself keeping it in character. Mind you, I write AUs and cannon stories and have fun with both - and difficulties with both, depending on the situations I put the characters in and the characters' own personalities - and I like to try my hand at rare/odd yaoi pairings if I think I can possibly do them justice. (This has made for a number of...let's be nice and call them insane...drabbles in the Bleach category, but as I and my readers tend to find the things entertaining, that's praise enough.)
There's a wonderful lady on AO3 who goes by blackkat (she's black.k.kat on FFnet) who let me adopt a few of her stories.... One of them is only slightly AU, but the other one (a Bleach story) has the Zanpakuto as dragons. Kat called it a crack story, but either it was really addictive crack or those of us who read that particular one of her 64 Damn Prompts were just completely taken with the notion; I have no few readers who came to my Inconceivable from her Incalculable and enthused that "Someone's continuing Kat's dragon story! Yesss!" She left such a wide area open for expansion that I'm having a blast with it. Zanpakuto personalities as dragons, capable of independent action.... Makes for tons of awesome. Plus the whole world-building thing, since I like to take bits of canon and mix them into the AU plot line.... In one way I guess you could say that doing so is cheating, or makes it easier, but the thing about mixing canon details into an AU story is that first you have to know how much is too much, how much should be discarded. And then you have to figure out how to fit it all together into one story. Complicated and time consuming, but ultimately worth it.
I don't stick only to medieval AUs, either. Took on a challenge from Clara Barton on FFnet; she wanted someone to write a Gundam Wing/Three Musketeers crossover. Normally I can't stand crossovers (because they are so very, very rarely done well), but this idea reeled me in before I knew what was what. So in order to combine the two series and their respective plot lines, I had to make it a futuristic AU - and while I'm only now working on the second half of the prologue, it looks to be insanely entertaining. And after talking it over with Clara and the other wonderful woman who expressed interest in the crossover (and is a friend to both myself and Clara), I decided to draw from the Disney version of The Three Musketeers...on account of I can't do anything without humor and the Disney version is funnier than most. It's an insane and somewhat daunting task (I had to scrap most of the medieval and current societal layouts entirely and create the system I'm using nearly from scratch) but it's so very fun. The first half of the prologue reads like a movie trailer, so Snow and Clara tell me.
Simply put, AUs are wonderful things when done right - but often enough they aren't, so I...dabble.... I read a few chapters if the summary interests me, and if it seems good then I'll run with it. If not, hey, that's fine too. I'll just leave. Why make my eyes and brain suffer through something I'm not enjoying?