Last night I downloaded Paul Kingsnorth's debut novel The Wake, which is on the long list for this year's Man Booker Prize. I'm not really into literary fiction, but this is also genre fiction, which I do love. It's set in 1066(and all that, okay, it STARTS in 1066) and is not about celebrating a dead person's life but about a rebellion in the fens country against the newly arrived Normans. It happened. The story of Hereward's rebellion is a part of history, though it's been fictionalised a lot. Actually, there was a wonderful, beautiful novel, Saxon Tapestry, by Sile Rice, which I read while playing mediaeval church music to get me in the mood.
But this is different. I've only started reading, but the novel is in Old English - sort of. Even the author admits he had to play around with it or it would be even harder to read than it is. He cals it a "shadw language" that gives you the feel of the real thing.
Now, I did a semester of OE at uni, though I ended up focusing on Middle English because you couldn't do both and I was interested in doing my Honours thesis on King Arthur and Malory wrote in ME, not OE. I was quite good at it in the limited amount I did, because I had a background in Yiddish, which is related to mediaeval German, which is related to OE. So I'll manage this book a lot more easily than the average Joe or Josephine and even I'm going to take a while to finish it.
That said, I've found through reading it aloud that the general text and the dialogue is basically in modern English without the slang. If it wasn't using OE names and spelling for things, it really wouldn't be too hard, so stick with it. You'll get the hang of it. I'd suggest the ebook version, as the publisher has, I believe, done it as a manuscript between stiff cardboard covers and when you just want to read a book on the way in to work, that could be a nuisance. But up to you.
It is, anyway, a brave experiment by the author. He could have sold it to a regular publisher if he'd just written it in modern style but he refused to change it and ended up instead going with a small press, Unbound, that has the policy of asking the author to crowd fund his or her book. He managed to get 400 pre-orders and here he is, up for a huge prize! Clearly his faith in his book as it was worked out.
I don't blame him, anyway; it must have taken a HUGE amount of research to get this done, not to mention getting the style just right. No convenient spell or grammar check on the computer - actually, you'd have to turn it off or go crazy.
Good luck to him!