From my reading, Carcassonne has several expansions. I bought Inns & Cathedrals because I believe it adds the most depth. The Dragons & Fairies (real name?) is just fluff randomness. The other one I can't recall is a close 2nd behind Inns and Cathedrals.
The game is fun because you get to build stuff. You don't have to worry about hand management since you only ever have a hold on one tile. The only hard part about the game will be both of you learning the "Farmers" rule. It's the only abstract one and it'll probably take a few read thrus to get it. I am still not sure I'm doing it right! haha