The Green Pearl is a much better book than I recalled it being. Perhaps that's because we spend some time in an alternate world, and Vance is thus freed from the constraints of Earth. Perhaps it's because the storyline is simpler, following primarily Aillas and Glyneth.
Aillas, King of Troicinet and South Ulfland, spends a fair amount of time haring about on his own adventures, which requires a certain suspension of disbelief, but credibility is not really a major factor with Vance books. The focus on individuals brings Vance more truly to his own territory of longing and lust, of weird creatures and places.
The politics remains from Suldrun's Garden, but here it's more straightforward (Aillas protecting his land) and less obtrusive. The book spends less time describing Lyonesse overall, and more on individual adventures. It's a much better book for it, and much more Vancian.
The Lyonesse trilogy is a good introduction to Vance for those who are used to somewhat more traditional narrative. For Vance aficionados, this is not his best work, but it's good.