Beautiful and fluid, with a great story, but is far too short.
The story is compelling and enjoyable and improved only by the excellent voice acting. Every character is acted - from voice to movement and facial quirks - with near perfection, from the endearing Kai (who is one of the best game characters I have seen in a long time) to the delightfully evil King Bohan (Andy Serkis).
The gameplay is great, too. It's filled with combos that are not absurdly complex, but not button-mashingly simple. Some of them are absolutely jaw-dropping when performed (not to mention, ball-wracking). And one of the most enjoyable parts of the entire game was using the SixAxis motion controller to direct the "twing tang" (bow and arrow). Hands down, the best use of six-axis I have seen.
As much as I loved Bioshock and its wonderful retro look with atmospheric dystopia and in-depth story, I would be compelled to place Heavenly Sword on-par with it. The story is not as deep, but I found it more compelling and engrossing during play.
Alas, the game was definitely too short and some of the "boss battles" were - while not simple - rather plain. That is, they were occasionally difficult, but they were nothing more than "watch for the weakness and then exploit it when the bad guy conducts his repetitive movements and attacks". I would have preferred much more intelligent bosses.
I can't wait to play the rest of the trilogy and I hope they find a way to bring us more Kai!