The best feature in Sun of Suns is really the setting. The author has created a believable universe set inside a world-sized baloon, with fusion-operated suns, floating cities made of wood and metal, forests, asteroids, cloud banks, even animals... the descriptions are detailed, well thought-out, and grab the reader, not wanting to put this book down until the very end.
The characters are manageable, with enough depth so as not to become too stereotypical.
All in all, a very good read, a nice adition to any sci-fi library, and a great introduction to an interesting universe.