Since this is an expansion review, I am assuming familiarity with the base game.
The centerpiece of the expansion is a board extension that adds five more areas that resolve in the action phase (between actions 9 and 10 of the core game).
Four of the areas are places for master builders:
9a: Grants exemption from taxes and collect income equal to the tax roll.
9c: Allows you to use any craftsman this round at one less than normal capacity. This can be one of your own that was already used or one of another player.
9d: You can sell any combination of resources at one more than normal market prices.
9e: Another slot for privilege cards. They are now separated into two categories (permanent in one pile and immediate or 1x in the other).
The remaining new area (9b) has four spots extra workers can be placed for victory points.
It also includes new event, craftsmen and privilege cards, as well as all the components (and rule modifications) needed for up to two more players.
My Overall Impression:
I'm a big fan of The Pillars of the Earth in the first place, so I was both extremely happy and a bit surprised to find that this expansion enhances it significantly. Initially my main draw to this was expanding the maximum number of players to 6 (which is done well and doesn't unduely slow down gameplay) but it's a lot more than that.
The game balance is made even better than before, with the new action spaces and cards adding well developed additional options. It all fits seamlessly into the base game without disrupting flow or seeming superfluous.
Most impressive is the fact that the board extension and new cards are perfectly usable even if you just want to play with the traditional 2-4 players, which again makes it significantly more than just a additional player expansion (not that the extra player part itself isn't greatly appreciated).
Everything here not only fits in with the original game but adds to it significantly and this should pretty much be an instant purchase if you enjoy the base game.