Good books can demand your attention and can broaden your knowledge. Ivanhoe does both. While it does not aspire to the higher thoughts of some great authors, it's daring adventures, brave heroines, carefully crafted villains and all-star cast of extras (including Robin Hood, Little John and Friar Tuck!) is satisfying and fun!
I just finished Ivanhoe today (while I was supposed to be doing other things like grade papers) and it has wound itself into my list of favorites! The language is a bit ponderous for such a light romp, but it was written long ago - and is well worth wading through. It'll be on my short list of Middle Ages literature requirements for my kids when we reach that time period.