I enjoyed this book, but I can see how some people might be completely disinterested in it. It's a story about loyalty to a cause, a person, an ideal, these are things that I think we've forgotten as a people and I think that's why I enjoyed it so much. I think part of the reason that so many people don't enjoy it is that it's hard to associate with a group of people so bent on avenging their lord's death that they know that they'll die at the end of it whether they're successful or not. That's just not how we live our lives these days and it's incredibly hard to associate with a group of people like that.
Still, there is another reason to not like this book: the prose is stuffy and the lives of the people we follow are pretty flat and one-dimensional. I think there's a valid excuse there too, this was a piece of history that became a play and some depth would need to be removed for that medium.
Then there were times in the book where things were slower than others, parts where you were waiting for something interesting to happen. Here I feel like we're in the same stasis that Oishi—the main protagonist—is in and we suffer with him.
All of these things are negatives, but they all have their reasons and excuses and at the end of the book, I can say that I truly enjoyed this book. It was worth my time now and will be worth my time again. It's a parable or a proverb about loyalty to a cause and the things in life worth dying for. You might disagree with Oishi and his ronin, but they knew in their hearts that their master's revenge was worth their deaths.