Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Ivanhoe's tone is pretty unusual. Even though there's a lot of realistic description of appearance and clothing to help the reader imagine the looks and manners of these medieval characters, every dense description is very emotional. Consider the passage below, taken from Chapter 43, when the Templars are leading Rebecca onto the tournament grounds to await her trial by combat:
After these neophytes came a guard of warders on foot, in the same sable livery, amidst whose partisans might be seen the pale form of the accused [Rebecca], moving with a slow but undismayed step towards the scene of her fate. [...] A coarse white dress, of the simplest form, had been substituted for her Oriental garments; yet there was such an exquisite mixture of courage and resignation in her look, that even in this garb, and with no other ornament than her long black tresses, each eye wept that looked upon her, and the most hardened bigot regretted the fate that had converted a creature so goodly into a vessel of wrath, and a waged slave of the devil. (43.32)
This passage is largely a portrayal of Rebecca's appearance: her beauty (of course, since Scott can't get enough of the pretty ladies) and her simple clothing. Some novels might be objective and distant in describing a character's appearance, but here Rebecca is "undismayed" by her fate and shows an "exquisite mixture of courage and resignation." Not only is Rebecca exquisite (not really a neutral term), but "each eye wept that looked upon her": she looks so lovely and brave that everyone who sees her cries at the sight. Scott wants to build up our sympathy for Rebecca here. This passage gives a precise description of her outward appearance, but it also includes subtle, positive value judgments about her loveliness and bravery that shape our perception of her character.
This is why we say that the tone of Ivanhoe is emotional. Not only do the characters feel a great deal over the course of the book, but every paragraph – even the relatively dry ones that set the scene or give background information – contains emotional language to influence our feelings about whatever is being described.