The final book is this series is the best possible finish. It could not be improved anywhere. Excalibur is exciting from beginning to end, and as with the first to books, it is so easy to get caught up and enveloped in Cornwell's story. Throughout all three books, I had to be careful reading it in the evening, because when I would finally put if down, I'd realize that four hours have past and I've got about another four to sleep for work the following day.
Excalibur is just as unique a story as the first two books. The story is original all the way through. We are only familiar with the characters' names, but not with the characters' characters (or personalities, but I thought that was funny.) For example, Arthur is a pagan, not a king, and never once says the word "Grail." Lancelot, who we are used to seeing as a man to rival the goodness and skill of Arthur, is a deceitful worm, lying and cheating his way to power, and ends up betraying Arthur. I don't really know what I thought of Merlin before this, but now, he's a man just as magnanimous as Arthur, but much more a zealot (Merlin IS a Druid though.)
To me, the ultimate test a book can face is whether or not it has me in tears by the end. Les Miserables did this to me, and that's one of the greatest works in history. The end of Excalibur put tears in my eyes and a lump in my throat. It's finish was so fitting, so perfect, and still so disappointing. Not disappointing in the sense that the author failed in some way, but disappointing because we feel for the characters so much, we can't help but mourn with the characters with the great sadness thrust upon them in final chapters.
Definitely the perfect finish to a perfect series. No book in the series is better than the other, but each one will feel like the best when you're reading it. I have two wishes with this series. One, to find some one else who's read it so I can discuss it (something I love to do with books), and two, personally tell Bernard Cornwell how good I thought these books were. I'd recommend them to anyone in an instant.