In reaction to Jenny's interesting post, I'd like to add some thoughts on Doré's and Phillips' illustration solutions. In my opinion, the best illustration is one that adds to the text, not only depicts parts of it. If the illustration fails to have a catchy concept, you better make sure it looks amazing, in other words; if you haven't got a great idea, compensate with technical skill. If both are in the mix you hit the jackpot.
Tom Phillips take on Dante's poem demands a lot of participation from the viewer and therefore might be more interesting from the artistic perspective. It is like comparing a Hollywood production to a Lars von Trier film.
In Doré's case, I think he overpowered the original poem. As jenny said, no need to read no more! This would be a sad thing for the writer if this was a new story being told, but this thing was written about 550 years before Doré took his turn on it. It was going to be his party!
A contemporary example of this is the take on Frankenstein by Bernie Wrightson. Everybody more or less knows the story, so he goes crazy on the drawings. Clearly inspired by the engravings of Doré, he depicts the classic story in pen and ink, not being too conceptual, but visually overwhelming. Wonderfull eyecandy. If this would have been made before the film he would without a doubt have set the visual standard on this classic tale. Bernie Wrightson's Frankenstein may be an iconic book, the visual standard had already been set by Boris Karloff in the 30s. His monster is the true icon.