Kalamar is decent, but I prefer Scarred Lands.
Kalamar has a flavor very similar to old school Greyhawk, but is reworked from the ground up to provide for better internal consistency. The core setting book is a little dry to read, as there are few easily identifiable overarching and easy to grasp themes but lots of little details. If rich detail fits your palette, you may like Kalamar alot. Also, if you are a map fiend, the maps for Kalamar are, IMO, a lot better -- more attractive, more detailed, more true-to-life. Further, Kalamar has a lot more adventure support, though some of those adventures get bogged down in details.
Scarred Lands is much easier to digest and goes further from the basic D&D formula. Make no mistake -- despite what KDLadage implies above, Scarn is richly detailed, internally consistent, and has a well thought out history. Scarred Lands doesn't tow the geographically true-to-life line. Geography in Scarn is directly influenced by supernatural upheavals -- a sea flows with the blood of a titan and some mountains are said to be teeth of a titan. IMO, Scarred Lands is better fantasy because it is more richly immersed in fantasy elements.
Finally, if you are a rules fiend, I find the rules content in Scarred Lands books to be better than KoK books in general.