I do like this expansion, but after a few games I was able to quickly see some flaws, or at least annoyances that come up in our games. A few have already been mentioned in others' reviews.
Here's my review of the specific elements:
Abbey - nice piece for finishing, a nasty piece for aggressive strategy. I had an opponent in a stranglehold until this nifty abbey came out and scored a pile of points. The tiles are not nice enough to me to allow more than one significant block per game. More than once I caught my opponent(s) in large cities with multiple knights each that were sure to be stranded, only to have an Abbey save the day and free them all. It takes skill to set up those blocks! It takes nothing to drop in an abbey and pile up the points.
Mayor - so far, so good! A key mayor placement results in some epic control battles and a load of fun!
Wagon - has some use, scores some points, an ok piece.
Barn - Maybe I'm just horrible at drawing tiles, maybe my opponents aren't smart enough to block farms very well, but one player usually places the barn early in an open place, defends that opening with small cities, cloisters, and other non-blocking pieces, and always succeeds in making the largest farm and scoring piles of points. I was able to snipe bonus points 3 times in one game by connecting new farmers to the existing barn-farm, but the point difference was still staggering.
I think the strategy of battling farmers for numerical dominance is much more fun than the big barn-whammy attack.
I know people who play this game just for fun, and build to score points. I play strategically and enjoy the thrill of battle. Thus, I like the Tower because you have to be careful in meeple placement, and I like logically solving where to move the dragon in P&D. The Mayor in this expansion rocks, but the Abbey provides easy escapes and I think the barn is too powerful as well. Depleting an opponent's supply of followers is a key strategy, and the barn and abbey wreck that tactic.
So that's a summary of the several games I've played with this expansion. Does anyone have more positive stories?