The Abbey and the Mayor feels more like a collection of mini expansions rather than a bigger set, so I feel it is best to review it by its parts.

The Abbey:
Not a meeple, but it commands attention. The Abbey will probably go down as one of the most controversial components in the world of Carcassonne. It essentially eliminates the chief defensive strategy of blocking off your opponent's cities and thus preventing closure. In fact, some players will find themselves intentionally blocking off their cities near end game so they can close them with the Abbey. As a result, players will tend focus on their own cities. Those who prefer a more non-competitive live-and-let-live approach will love this addition.

I was surprised that the Abbey adds almost as much to the game as it takes away. It can even be used as a great handicapping tool by alotting one for new players and zero for experts.
My rating: 8/10


The Mayor:
The mayor, heretoforth known as Hammerpants, is like an inflatable fatty meeple (from Inns and Cathedrals). Though restricted to cities, rare is the play where he's worth zero. In fact, the true impact of Hammerpants's prowess is felt in games also using Inns and Cathedrals when Hammerpants, Fatty and Meeple Regular battle it out. Otherwise, the addition to the game is relatively minor.
My rating: 6.5/10


The Wagon:
The great movable meeple. The wagon's only restriction is it cannot be used as a farmer. Otherwise, it can travel to open cities, cloisters and roads whenever the feature on it is scored. Since moving occurs after scoring, you can play a meeple, score the feature, then move the wagon. Fans of road-building, or anyone suffering from a case of empty nest syndrome (i.e. out of meeples), will benefit the most from the wagon. In the end, the points earned by moving it will only matter in the closest games.
My rating: 6.5/10


The Barn:
If Phil Rizzuto's body was reanimated and taught Carcassonne, his corpse would vomit his catchphrase all over the barn. As if farming and field wars weren't game breaking enough, Hans im Gluck dropped this bomb on us. Deploying a barn isn't easy, it can only be placed where 4 corners of a field match up. However, it doesn't matter if there are meeples already tilding that land. In fact, this is a major component of the barn's power. Once placed, all meeples in that field are scored according to 3rd edition rules and returned to their owners. As a barned field connects to other fields, any farmers on those lands are also scored, but this time only for 1 point per city. At end game, the barn scores 4 per city on that farm.

The potential for the barn is massive. In fact, playing with this and the base set alone, it's possible to score 7 points off one city (20 if you mix in Traders and Builders, the River II and The Cathars). Do you place a barn on fields your opponents control, or do you do it to fields you already farm scoring 3 per city now and 4 later? There are so many fun scenarios that can arise from the barn that it makes up for the possibility of the piece being broken.
My rating: 8.5/10


Overall:
These components, as well as some spiffy new tiles, combine for the best expansion since Traders and Builders. Resource management isn't such a concern since there are three new meeples, one of which can return your farmers back to you. This is a positive or a negative depending on your preference. Save for some ambiguity regarding the Abbey (can it be played even if there are no regular tiles left?) the rules are concise and easy to pick up.

Overall, the set is a throwback to the kindler, gentler days of Carcassonne before the Dragon, Count and Tower instilled some evil--but fun evil--into the game. This is highly recommended for any Carcassonne fan.
Final rating (not an average): 8/10