I hadn't heard anything about Kingdoms of Kalamar prior to recieving the campaign setting, but I'm quite impressed by it. Ever since I started DM'ing about a year ago now I've been running the default Pathfinder Setting of Golarion. I really like Golarion, but I didn't really realize how pulpy it was until I started to read Kingdoms of Kalamar. Some might call this 'Generic' Fantasy, but honestly this book is a very strong vibrant campaign setting, and has a really fun feel to it. The box hypes the 'realism' of the setting, as far as geography, ethnography, weather patterns etc go, but those categories don't make a good game world on their own.
The 'realism' I noticed most in this book was how realistic the motives of major NPC's feels. I've only read the first section of the campaign setting (Brandobia), which has 4 human nations which once were part of a great human empire. These humans settled on the Northern continent of Telene long before other Human races migrated north from the "cradle of Civilizations" and were taught the ways of Magic and archery by their elven predecessors, and of agriculture and other civilized ways by the halflings. The Brandobians soon forgot their debt to these cultures and attempted to overtake the Halfling and Elven domains. The Elven kingdom repulsed the entire human nation's attack, embarrassing the King greatly. The King blustered about the elven nation, and when the Elven King heard about this, he 'blessed' the King with fertility. Shortly thereafter, the queen conceived three sons. These sons grew up to manhood and when their father died, they quarreled for the right to become king. Brandobia was split into three Kingdoms. As I was reading this section, I was mentally comparing it to a similar story in the Eberron campaign setting. Both stories are similar, and provide a lot of fun roleplaying potential for the PCs. The story of the Kingdom's fall in Kalamar reminded me strongly (in a way that Eberron did not) of the tales of elves and fae in European history. It read like a fairy tale.
Over all my impressions of this book so far are very favorable. It feels like a campaign setting for the Hobbit before the Lord of the Rings, a traditional fantasy world in every sense. I've seen some reviews which use this to stigmatize the setting, as a boring generic world. Kalamar doesn't seem boring to me at all, it is very close in feel to an old fairy story like Hans Christian Andersen or the Hobbit in many parts. As I've begun to read the next chapter, on the fallen empire of Kalamar however, I'm seeing more gritty influences that reminded me of the War of 5 Kings in the Game of Thrones series. This campaign setting is really good reading so far. I would highly recommend it for browsing, or for running a campaign.