Carcassonne is a mainstay in boardgaming circles. There are lots of reviews of the boardgame elsewhere (and hopefully by others in this thread), so I'm just going to talk about the XBLA implementation of the game. Also, it should be noted that I'm playing this on a 4:3 SDTV.

Screenshot from the 16:9 version.

Cons:

• Wasteful UI The game has two primary methods of indicating who the active player is (see pic). 1) The little colored circle to the left of each person's score. That circle will glow for the active player. 2) The score box of the active player is twice as wide as those of the other players. Even though the score boxes are semi-transparent, you will almost always shift the board around to view what's under them. By the midpoint of the game the board is very busy. So any extraneous visual UI will only detract from usability, and this is especially true with the double-wide active player score box. Also, as Danjo mentioned earlier, there's no way to tell who is speaking.

• Stepped zoom The zoom function uses discrete stepped maginifications rather than a continuous scale (like Catan). There have been many occasions when the most useful level of magnification has been between two of the arbitrary zoom levels. The fact that the game animates a smooth transition between any two zoom levels proves that a continuous scale zoom is possible with the engine, so there's no apparent excuse for this.

• Lack of multiple local players support over XBL Honestly, why?

• Pawn (meeple) type It is sometimes difficult to discern whether a pawn represents a farmer, a guy on a road, a guy on a cloister, etc. In the board version, it is conventional to lay a pawn flat to indicate a farmer, and the XBLA version does this too. However, an opportunity was missed here. The boardgame uses generic pawns for cost reasons. The XBLA version doesn't have that restriction (although it might have a legal restriction), so they could have made the pawns a different shape for each of the roles.
  

Pros:

• Legal tile and pawn placement As soon as you draw your tile, the legal placement locations are indicated. Once you place the tile, your legal pawn placements are indicated. This might not seem like much, but that recognition takes time in the boardgame. Also, when you bounce your pawn around the available spots, it highlights the entirety of the area it would influence.

• Speed The XBLA version takes roughly 20%-30% less time to complete a game.

• It's Carcassonne This is the big one. The foundation of this game is as solid as they come. It's fairly casual, but extrodinarily flexible. It plays just as well for 2 players as it does for 5. You'll never have to wait for a quorum to start.
  

Conclusion: On balance, the XBLA version of Carcassonne is a good rendition of an excellent game. Buy it.