Carcassonne is a popular casual Eurogame that many gamers use to introduce modern designer games. Carcassonne's strength is the simple yet engaging rules. On your turn you draw one and play one tile, optionally you can place your "meeple," a follower token for scoring. The decisions are simple since one edge of the tile must match the edge of a previously played tile to create a consistent landscape. However some gamers prefer something more meaty and can add any of a number of expansions to add more depth. Expansions range from intriguing to ridiculous such as the, Carcassonne: Catapult -- you fling tokens with a chopstick sized, wooden catapult. However adding expansion breaks the core simplicity by adding more fiddliness.
Caracassone: The Castle is a reworking, a sequel to the original Carcassonne by Reiner Knizia and with Klaus-Jürgen Wrede, the original Carcassonne designer. Although the core gameplay remains the same -- draw-one, play-one -- Caracassone: The Castle is a much deeper game. The theme is also the same, you run a medieval temp agency, sending workers to short-term contract jobs. Key differences are: no edge matching, two-player only, static boundaries, and complex scoring. The game is set up by building outer walls that create an outline of the the castle. The walls do three things: create a defined tableau, offer seven start spaces that tiles can be placed next to, and serve as a scoring track numbered 0-99.