The idea of a hero going home, wooing his true love, and fighting bad guys wasn't original to Scott—Homer pioneered that plot much earlier. Nor was the idea of framing the story in an historical setting—the Irish and Icelandic sagas are essentially historical novels in that sense. What was unique to Scott was the blend of actual historical figures and events with those of his own creation and those of legend and folklore. Some of the best parts of Ivanhoe—and the least expected—are the scenes featuring the Outlaw of Sherwood and his merry men, including a particularly aggressive and hungry Friar Tuck.
By uniting myth and historic fact Scott lends context and opacity to both, building a vivid stage on which to direct his story. Today's historical novels focus on the setting itself as being of most interest. They pile detail on detail, the result of months of research (sometimes years), so we get a good feel of time and place, but too often the narratives are less than compelling. It's not Richard the Lionheart or the futility of the Crusades Scott wants us to think about, it's something more human and universal. These elements offer credibility and realism, not the substance of the novel.
Ivanhoe is really about race relations. Most obvious is the tension between Norman and Saxon in post-conquest England, as the native Saxons are oppressed by the French newcomers. This uncomfortable situation is present from the beginning, when members of both races converge at the castle of Cedric the Saxon. There is also the more remote struggle between Christian and Muslim in the Holy Land—this serves as a foil for the Norman/Saxon relationship, as all Christian parties (Norman and Saxon) are united in hatred of the heathen Arabs.
But Scott does something much more bold for his time. Throughout Ivanhoe, the eponymous knight is helped and abetted by the Jew Isaac and his daughter Rebecca. In Scott's own day, but even more in the Middle Ages, Jews in Europe were considered a sub-race, at the best second-class citizens filled with avarice, cunning, and evil intentions. Scott's treatment is beyond sympathetic, it is positive, portraying Isaac and Rebecca as the most human, most caring individuals among a crowd of self-serving, vicious knights and churchmen.
There's fun stuff too, of course, not just incisive commentary. Lots of action, for one thing—meleés, jousts, fistfights, sieges, and battles. Romance, too, and sinister villains (Brian du Bois Guilbert is one bad baddie), intrigue, chases, damsels in distress, the works. Wamba, Son of Witless, Cedric's jester, is one of the most lovable and hilarious characters in literature; his priest-impersonating exploits are particularly memorable. And though I referenced Scott's dense style, his prose is carefully crafted and oddly adapted to his Medieval subject. Regardless, as one of the earliest examples of a modern novel, reading Ivanhoe is necessary for a good grasp of English literature, even if it's not always as thrilling as Tom Sawyer made it sound.