Great kingdom building for sure - but difficulty in obtaining citizens makes this game more annoying than it should be.
At this point you should know that in KfK, the goal of the game is to grow your kingdom by progressively obtaining schematics for different & more complex buildings, and the channeling your resources into different products to construct those buildings. While you start with a handful of Keflings and 1 or 2 schematics, you eventually grow to cover your entire map, and reacher ever more refined materials to get you there (ie. logs to lumber to carved wood etc). The pacing is well done - there are no enemies and with plenty of infinite-resource locations, you have virtually all the time in the world to build your kingdom at your leisure.
Unfortunately, the smooth gameplay is interrupted at a couple of points which, at least in my experience, detract from the pleasure derived from the play here. In the first case, you must always be focused on increasing the number of citizens you have. This is critical in that most buildings require a Kefling to "staff" if, as it were. So if you want to build a Brick-making building, you'll need to make sure to have an extra Kefling to install there. This means that expansion is explicitly limited to your population. Unfotunately, you cannot manually increase your population. Keflings only appear when you build a house and install a "heart" in it - since hearts are pretty rare that means that while you may have, say 20 Keflings after 4 hours of play, you may only have 28 Keflings at 12 hours of play - really stretching what you can actually do.
In the second case, the game forces you to totally clear all resources off of the map, in order that you may discover upgrades, valuable hearts, etc. This means that, while you may want to sculpt your kingdom around the natural environment (especially the forests) such action will cripple your ability to grow later. And while you can build a building that will build trees for you to plant and pretty up your kingdom, they don't match the original natural scene. All this means that, aesthetically speaking, you're limited in specific ways which I felt detracted significantly from my enjoyment.
That said, Kingdom for Keflings is certainly a decent game, and worth playing if you're looking for a relaxed-paced kingdom building game - as long as you don't mind clearing the nature around you and stretching your Keflings as far as they will go.