Hero was the first movie I've seen in months, so I'm glad it was a good one. Not perfect, but well worth seeing. I won't give away any of the story (although that's not the reason to see it). Instead, a few comments on the style and cinematography. In short, it's a beautiful film. Do not go in expecting a typical martial arts movie. This is more an art film with swordplay thrown in (there's no hand-to-hand fighting; it's all weapons). The really striking thing about the movie are the incredibly vivid, nearly monochromatic scenes which are the modus operandi of the film.
There is a framing device where Jet Li's character tells his story to the emperor, then the emperor retells it how he believes it happened. They go back and forth like this, telling almost the entirety of the story in flashbacks. However, each telling is different both in substance and color (though not style). In this respect it reminded me, to a certain extent, of Rashomon, which was likely the intention. Almost every scene has in it something visually stunning. The fights are elaborately choreographed, but easy to follow. The fighters fly around much like those in Crouching Tiger, Hidden Dragon, but in a more stately, dramatic fashion.
This leads me to the one major flaw I felt marred the film—the melodrama. The way the plot is told fails to withstand the emotional weight of the characters. In attempting to create an epic myth of China's creation, the director has the actors come across as too distant and serene. This makes the tragic scenes seem overwrought and shallow. However, if you take your cues from the incredibly stylized cinematography and formal mood it creates, it's possible to reconcile the unrealistic acting to the film by seeing the acting as another of its iconographic, stylized aspects. Even so, be prepared for some outsized emotions. However, it's not such a serious flaw that it ruins the movie.
Notice that I've said little about the actual martial arts. That's because it makes up far less than half of the movie's ninety minutes. Do not expect it to be action-packed. Although the fights are beautifully done, they are spaced considerably farther apart than one might imagine based on the trailers. This seems to be enough rambling about the movie for you to get a decent sense of what it's about though, so I'll finish. Overall, I highly recommend seeing Hero, provided you like pretentious art films masquerading as martial arts movies. I do, so I enjoyed it.
UPDATE: Pejman reviews the movie as well, but with spoilers.
I haven't seen the movie, but a commentor at Pejman led me to look around a (very) little bit, and there's a rumbling non-consensus that it's a piece of Chinese imperialist agit-prop. Here's a decent roundup:
http://www.gnxp.com/MT2/archives/002667.html?entry=2667
To that I would say, "well duh." Not that I noticed it while watching it, but in retrospect, it can certainly be viewed that way. Even so, it's an enjoyable movie.
I'm pretty excited to see it. The clips I've seen so far have been extremely impressive. It doesn't really bother me that there isn't much marital arts--I often find martial arts boring without a certain fantastic aspect (anime or outrageous special effects). Kill Bill, for instance, nearly put me to sleep.
Oh, no you di-ent.