It was very nice to see the range of classes, and that all the attention wasn't given to Kai Lords, but they're still my favourite. They're like medieval Jedi or a cross between knights, rangers, samurai and ninja!
And in terms of the mechanics, they are the most versatile character class. You could have a group of 4 Kai Lords, and each one would have different Disciplines taken at different times, giving each one his or her own specialties. With a couple of the other classes there is little room for variety, and by the uppermost levels, many that do have choices of advancement will all have pretty much the same abilities.
Put it this way: Kai Lord is the only class that could work if the entire group were made up of it. Which is good since I'm planning a campaign that will start based around the training of Kai at the monastery.