Each new Dominion expansion box takes the game to a new level, adding a new twist and more depth. I like Hinterlands because there are so many cards that have triggered effects, something that happens when you buy it or when another player does something. I've combined this with the base game as well as other expansions and it plays great. Don't think you have enough cards with the other expansions. This is an essential addition to the set.
The theme of this expansion is one-time effects, but the overall flavor of the game fits in beautifully with the base game and its previous expansions. This is definitely a great one to check out. Great variety.