The Hundred Thousand Kingdoms sounds like pretty typical high fantasy from what I've read about it. What makes in unique and worth reading, in your opinion?
Well, it is high fantasy in that there's magic and gods. Very active, very vocal, gods. I'm not sure it's "typical". As far as worth reading? Well-written, engaging, entertaining story. It's a non-standard setting, with fairly non-standard characters, and a much stronger mythological aspect (within the story, not in reference to real Earth) than is usual.
The first book (which is
The Hundred Thousand Kingdoms, my mistake - the trilogy is called the Inheritance Trilogy) was nominated for a Hugo (Best Novel), Nebula (novel), won a Locus for Best First Novel, nominated for World Fantasy Award.
I guess if you consider it "typical", you're going to have to clarify what you're looking for, whether it's just "no knights", or "no pseudo-European setting", or "no magic", or "must-have Indian setting".
Also, skimming the wikipedia entry - Sky is not a floating city. It's in a tree. A really, really, big tree. Shadow is the city under the tree.