This review is for the full Kingmaker adventure path, plus the map pack.
I recently purchased this product, along with the map pack, to run for my gaming group. This is the first Adventure Path I've taken part in and, in fact, the first canned adventure I've run since "the Red Box" as a kid.
This is definitely not the perfect adventure for every group. Many groups thrive on a high-octane, adrenaline-fueled story with a very clear ending and an exciting climactic ending. This isn't (always) that adventure. Those stories tend to be very linear, with the Player Characters filling in their part of the story without a great deal of branching out in various directions. Such a story is, by nature, linear, and therefore fairly confining in the choices offered to the characters, with most choices leading to the exact same result. That limiting nature is a large part of why I've avoided canned adventures (plus, I'm cheap).
Kingmaker, on the other hand, makes definite effort to be non-linear. The characters have a region to explore (with a decent reason to do so), then set up their own fledgling kingdom, which eventually grows over the course of the campaign into a substantial power. While players can go wherever they want (or not go anywhere at all, in some cases), there's definitely a push in certain directions. If your players ignore the hints to go east and randomly decide to go west instead, they'll run into encounters designed for a much higher level group, and end up dead. Also, quite a few events, especially later in the campaign, don't offer a great deal of choice. You either deal with the threat right away or watch your kingdom get wiped off the map, like so many of it's predecessors.
The downside of this non-linear approach is that a lot of the events aren't as linked together as they would be if your characters were being "railroaded" in a certain direction, and there's less tension in many cases. The upside is that players have more control of the game.
The adventures themselves have several strengths and weaknesses:
Strengths:
1) The kingdom-building rules are complex enough to be enjoyable and allow variety, yet simple enough that you'll be able to breeze through it pretty quickly once the novelty wears off.
2) I'm pretty sure every skill in the game is represented, noticably rewarding those players who take rarely-used skills.
3) Similary, there are a wide-variety of different types of challenges: straight up combat, sneaky assaults, plenty of politics, a tournament (in which most characters will have a chance to shine), mass combat, exploration, and, of course, kingdom-building. There aren't too many of the difficult moral choices that can make a political game realistic, but there are a few.
4) Online support. There's a Kingmaker Player's Guide at Paizo, as well as a fairly active forum for players and DMs running Kingmaker games to ask questions.
Weaknesses:
1) Some of the quest rewards are ridiculous. It feels very much like a video game mentality, where quest rewards fit the level of effort put into the quest, rather than realistic rewards that follow common sense. I'm scaling the rewards back dramatically when they don't make sense, and will make up for it elsewhere that it does.
2) The adventure starts with the characters already at their first destination, with little discussion of how they got there, and only the basic premise to explain why. I think it would have benefitted greatly from a section talking about establishing character motivations, and linking them to one or two NPCs they'll meet later in the game. I took the time to do this myself, and think it will pay off later with increased immersion and buy-in to the setting.
3) Many of the NPCs appear randomly right in the middle of the PCs city. A little extra effort on introducing them into the story would have gone a long way.
4) A minor quibble - the adventure path was put out before the Advanced Players Guide, so none of those classes are represented even though at least one would have fit perfectly. Paizo can hardly be blamed for that, but it's still a weakness for players today.
A note on the map pack - I thought this was a great idea for this particular campaign - a map with geographic details worked in but nothing else, so the players can map out their kindgom. But when I gave it to my players and told them they could write on it, they looked at me like I'd just stepped on a puppy. Many gamers are highly averse to writing on gaming products, and that will seriously hamper the utility of the maps. I also thought they could have chosen better locations for the location maps. The characters will almost certainly spend a lot more time at the Stag Lord's fort than at Varnhold.
Overall, I recommend that you carefully consider your gaming group, and if you think they'd enjoy a long, world-building campaign that occasionally lacks in urgency, this is a very worthwhile purchase.