The Last Enchantment (1979), by Mary Stewart, wraps up the Merlin trilogy. (It doesn't really, because she wrote more books, but I'll violently throw any temptation to read them out of my own head.) This book covers the foundation of Arthur's kingdom and his early reign in much the same way that a history teacher covers an era that he doesn't like but feels obligated to survey in detail.
If you've liked Mary Stewart so far, well congratulations, you're getting more of what you like. If you don't like Mary Stewart, you're either a masochist or an idiot. I'm both. However, I do admit that I cheated and skimmed most of the work. Even so, I found it overly long and dull.
If found that this book presented the least compelling story so far. To me, it seemed more like a survey of several important movements of Arthur's reign with no coherent through line to turn it into a coherent narrative. Stuff happens. It happens here. It happens there. It just happens, then characters talk about it a whole lot.
I can and will say just how pleased I am to be done this wordy behemoth. Good riddance. I hope to give the book away.