I had a few complaints about the farmers in Carcassonne. I changed the scoring slightly to make them less powerful and that worked very well, and the River tiles make it even a bit better, in my opinion. In the original, the early farms in the middle often yielded huge points at gameend. The River helps breaks up the middle of the board which helps contain farms a bit more.
I also play that the mountain at the end of the river goes all the way to the edge of the tile in the one corner where it is illustrated to be close to the corner. I make that another 'fence' for the farmer, not counting the small strip of grass that connects the 'north' side to the 'east' side. That means if the farmer really wanted to get a farm that reached around the mountain to the other side, he has to spend an extra diagonal tile to connect the fields.
Excellent addition. The River is so good that I enjoy Carcassone even without the Expansion as long as I have the River.