Fabulous. My son and I read it together and couldn't believe how good it was. Susan Cooper scores again; it's as good -- for a one-volume work -- as her Dark is Rising series. We couldn't believe how great it was.
My son and I don't understand why any negative reviews-- maybe a lot from the so-called misfortune of having to read it in school, rather than reading it because people loved Susan Cooper, or the Globe Theater, or London, or history, or even Shakespeare :) , and wanted to buy and read it for fun. If you read it for fun, it's totally heaps of fun.
It has a surprising and quite amazing ending too.