Guy Erma and the Son of Empire by Sally Ann Melia is a sci-fi action/adventure political thriller about a young prince destined to inherit his father's kingdom, and those who want to stop him.
Guy Erma has it all: power-hungry rulers, fragile interplanetary alliances, betrayals, shapeshifting aliens, forbidden love, knock-down-drag-out fights (sometimes literally), Battle Borgs, subterfuge, and don't forget the Gorans-- huge cats which are ridden by fearless jockeys and raced competitively (think Kentucky Derby, but with more hissing and growling).
Don't let the 400+ page count intimidate you. To have it all, and tell an epic story of two boys fighting for survival in a corrupt, uber-materialistic world where megalomaniacs in the upper echelons of society want them to fail, requires at least 400 pages. The book was paced so well I never had to slog through a chapter. More often than not, I was completely absorbed in our young heroes' plights.
Guy Erma is a top-notch entry into the canon of Sci-Fi Space Operas.