(My comments here assume you are already familiar with Carcassonne.) Traders and Builders is the second expansion to the original game and contains 24 new tiles. While a few of them are fields and roads (and add new things like bridges) most of them are city tiles. Some of these have odd and interesting corners that can help finish those awkward situations in constructing your city.
These new tiles, and few new rules, add another level of play. Now, instead of only striving to build your own cities, this expansion offers incentive to finish one that an opponent is working on. The city tiles feature symbols for the goods 'Wine', 'Cloth' and 'Wheat'. The player who finishes a city - your own or someone else's - that contains one of these symbols, collects a token for each commodity in that city. The player with the most tokens at the end of the game, of each of the three commodities, collects a 10 point bonus.
Other additions include one Builder and one Pig, for each player. The Builder pawn may be placed in a city or road under construction. Each turn that something can be added to what the builder has claimed, allows the player to draw a second tile. The Builder is removed from the board after that project is completed, and may be used in the same way again. Also, a player is able to place the Pig pawn in any field already controlled by a his/her Farmer. This adds an extra point to that field; so every city scores 5 points instead of 4...which may be just enough to push you into a winning position.
The final addition is a large cloth bag. Now it is easier to store and handle the tiles, as well as removing the problem of having non-identical backsides.
This game is playable with or without the first expansion - Inns and Cathedrals. However, it assumes that you own the first expansion as it does not contain the extra Followers to add a sixth player. (You do get a pig and builder for a sixth player, but you can only get the matching Followers from purchasing the first expansion.) In short, without Inns and Cathedrals it remains a 5 player game.
Overall, we felt this was worth the money and a great addition to an already excellent game. We liked the new 'twist' of wanting to finish off another player's city. Rather than trying to thwart their plans you may now have your eye on helping them get it done, because of the goods it contains. While the opponent still collects his/her points for the finished city, you get the token(s) and the potential for the final bonus. We found the Pig is more powerful then it may first appear. That added point (per city) has tipped the scales on more than one occasion. It can be a nice little strategic addition that can make for an interesting outcome. (Having said that, there are times when it appears useless.) Overall we felt this expansion truly enhanced Carcassonne. While it does add length, it also adds strategy. It made an excellent game even more interesting.