3 times better than 100
This movie is one part mother-effing ass kickery...

... and one part chick flick (but with nudity and lesbians)
300 is a fairly simple movie to synopsize: Three hundred of Sparta's finest conduct a suicidal holding action from an invading Persian horde.
With
that out of the way, I can get on with raving about how totally splendid this movie is.
Script: The first order of business in assessing a film's quality, in my mind, is its screenplay. As a writer myself, I am critical and judgmental about other people's work. There are plenty of excellent ideas and premises that fail because story was poorly delivered. All of that starts with the writing.
300 is an excellent story. It's premise is simple enough, but the depth of its characters, the multiple fronts of conflict and its poignancy all build on the foundation laid out in the script. (My only real complaint about the story was the less-than-satisfying and all-too-convenient resolution of the conflict between Queen Gorgo and Theron.)
Style: Like
Sin City before it,
300 has a very comic book style to it. The imagery is painted with a grainy and gritty overtone, with the colors in the scenes muted or otherwise altered to express the point of the scene. Obviously, many movies manipulate the senses in order to magnify a point or to make subtle one, but
300 does an excellent job.
Scene: There is a lot to be said for quality of direction. For me, direction is about deciding what each individual shot should look like. Scenes should not be disposable and they should not be filmed unless you have put some thought into it. A movie has only so many images to tell a story. When filming a shot, the better directors take that opportunity to make that shot stand on its own.
300 does this very well.

Nothing says “oh shit!” like a hundred thousand arrows raining down on you.
Skin: Check and check.
Slash: Much ass was kicked in this movie.
Sadness:
300 has its poignant moments. It's very premise is one of self-sacrifice. On that point, it predictably delivers. It's touching, because nobody wants to see the good guys die, even in a selfless and heroic context. However, I think the movie understands its role and its purpose and stays within its boundaries.
300 doesn't try very hard to be a metaphor about war or the human condition. A movie that has mutants, chick on chick action and shows least three slow-motion decapitations really has no right to wax philosophical about the tragedy of war, the human tendency for imperialism or back-stabbing and corrupt politicians.
On the same token, though,
300 takes itself seriously enough to... well... be taken seriously. It isn't a mindless action flick. It isn't a mindless chick flick. In fact, it wasn't mindless at all. It seems that everything you see and experience while watching the movie was supposed to be there. I think that's the way it's supposed to be.
Verdict: Totally did not suck