I'll get this one out of the way quickly. It's hard to write about non-fiction books, and I've never quite got the hang of that.
Read this one. It's an incredibly detailed biography of a truly extraordinary woman. It doesn't romanticize or embellish anything, but neither is it dry and lifeless. It would be hard to do that, with such an incredibly story to tell. Alison Weir does a flawless job of relating the life of Elizabeth I, from the moment she was became Queen until the moment she died. But she doesn't just list facts and gathers information from different books; she makes sure to connect the life of Elizabeth to everything that was happening at the time. You can't disconnect a person from the times they lived in, and trying to add modern sensibilities (I'm looking at you, Phillipa Gregory) just belittles their story and insults their legacy.
Weir did extensive research not only into Elizabeth's reign, she looked into everything that went on around her: how she dressed, how she walked, how she spoke, wrote and loved. She goes into great detail about the people who surrounded Elizabeth, how they were affected by her and how she affected them.
It's one of the best biographies I've ever read. A big, heavy book that took me (a pretty fast reader) almost a month to read. But I was never bored. I never got tired or had my mind wander. This book was so rich in detail that I would gladly read it again sometime. I can't recommend it enough.