It's heralded as one of the most epic campaigns ever published.
It spans about 80 years and handles multiple generations of knight player-characters, spanning the time between the middle of Uther's reign to the death of Arthur. It even covers advances in arms, armor, fortifications, and culture during the eight periods it addresses.
It contains writeups of many key locations, around 50ish creatures, tons of major NPCs, and incorporates a possible hundred scenarios (some are just adventure seeds, others more fleshed out).
The only complaints I've ever heard about it are that it lacks an index, and that at times, the scenarios have a lot of "your knights are there when this important thing happens", rather than being them participating in the actual events. It is not a ready-to-use book, but instead is a campaign road-map.