Nightfall is a new take on the rapidly growing deck-building genre, with several new and innovative concepts. For me, there are really two things that make Nightfall great - direct player conflict and the unique chaining system. The chaining system allows you to play cards not only during your own turns, which makes all players much more involved throughout the whole game.
One of the best of the new crop of deckbuilders, Nightfall mixes some of the best elements from classics like Magic: The Gathering and Dominion--without the booster-pack burnout of Magic. Tons of combat and player interaction assures that board game and CCG players alike will feel right at home.