I've read some books from Silverberg's Majipoor cycle, and enjoyed them immensely (they're Silverberg, after all). So, I was positively disposed towards this novel with illustrations from the start.
Note that I say "novel with illustrations," not "graphic novel," in keeping with FDA rules about listing the majority ingredient first. This is a textual main course with a side order of imagery - not a bad thing, but set your expectations properly. Even though I last read a Majipoor book years ago, I vaguely remembered enough to orient me to Silverberg's multi-species planet. It's beginner-friendly, though. You can dive right in as a novice and still get just about all of the meaning and undertone.
Illustrations are painterly and craftsmanlike, but not memorable. Rendering meets respectable standards and doesn't descend to gimickry. Poses tend toward the static, though, and a generally dark mood makes them hard to read in suboptimal lighting - like reading in bed, for me. Still, they enhance the enjoyable text, giving the reader a sum that's more than the parts.