The most important thing to note about Heavenly Sword are its controls: don't start playing the game, expecting it to control like God of War. This is a vastly different beast to tame, and button-mashing isn't as encouraged in this battle system. Expect to be a lot more methodical, and observational, as analyzing enemy movement and stances becomes crucial to true success in the game.
Nariko has control over three forms of the Heavenly Sword, each feeling drastically different from the other. In its default state, it forms two separate swords, which give Nariko the best overall speed and range. However, holding either L1 or R1 will change the sword into one of its other two forms. First;y, there's a chain, which is best for keeping large groups of enemies at bay. Secondly, the sword can transform into a massive blade, one which would make Cloud Strife jealous. Obviously unwieldy, this one will attack for massive damage.