Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Serious, Philosophical, and Emotional, with a Refreshing Twist of Comedy
We're in for Some Serious History
For significant chunks of the novels, White defaults to a serious tone that aspires to historical writing. The narrator's just telling the story of King Arthur, the famous English King, and how he grew up, came to the throne, and what later brought him down.
One place where we see this is in the passages where White provides historical background:
The Saxons were slaves to their Norman maters, if you chose to look at it one way—but, if you chose to look at it in another, they were the same farm labourers who get along on too few shillings a week today. (S.14.2)
We're also in for some serious philosophizing when the narrator (probably meant to be the voice of White himself) editorializes on Might vs. Right and on war. We're getting a healthy dose of political philosophy along with our history and soap opera.
Pay attention, also, to how the tone gets progressively darker in each novel. By the time we get to Candle, it's almost pitch black—it's just that serious.
A Bad (or Good) Case of the Feels
Don't forget that we're dealing with the genre of romance, so there are lots of highly charged and over-the-top emotional scenes. That scene where Wart stops Ector and Kay from kneeling down to him, right after he draws the sword from the stone? You've got to be one icy-hearted kind of person if you don't get choked up after reading that.
Along those same lines, check out this scene where Arthur and Merlyn are talking about the King's eventual death and what will happen to the Round Table:
"I wonder," [Arthur] said at last, "whether they will remember about our Table?" Merlyn did not answer. His head was bowed on the white beard and his hands clasped between his knees.
"What sort of people will they be, Merlyn?" cried the young man's voice, unhappily. (Q.10.45-47)
This image of poor old Merlyn crying into his white beard is touching, and not only amps up the drama but also creates a sense of empathy that contributes to the novels' emotional tone. This also takes the books from being strictly in the historical and into the personal… even though Merlyn is crying about the fact that humanity will continue to be violent and bloodthirsty way into the future.
Comedy
It can't all be doom n' gloom and heavy-handed intellectualism. The books have to have some lighthearted moments, and White uses these to give us some relief from when the going gets too rough.
So we get the award-winning slapstick duo of King Pellinore and Sir Grummore Grummursum, who have truly immature fights. And who could forget about the accomplished cosplaying crusaders, Sir Palomides and Sir Grummore, who, in one of the most hilarious scenes of the novels, make a Questing Beast costume to yank Pellinore out of his depression?