But I also half-suspect that 300 represents, if not another paradigm shift, then perhaps a paradigm consolidation. It became a hit even though it offered almost none of the traditional narrative movie pleasures: no stars, no twists or turns, hardly any "story" to speak of - just spectacle and digital effects and lots of it, done in a semi-facetious style that (as commenter Mega pointed out) never really earns the epic scale that the material suggests.
Vincent Baker calls it "dumb" and Dave McDougall thought it was "boring", and it kind of is by the usual standards of quality filmmaking, which is why I think, so far, Michael Blowhard has had the most incisive and perceptive take on the movie or, at least, on what the movie represents in a larger cultural context. You'll probably find your own key thing to take away from this piece, but here's mine:
Pre-computer movies often took you out into the world. As lovely as they could be to lose yourself in, they weren't an end in themselves. They were concerned finally with real experience, and they drew on culture in a broad sense: on art history, movie history, music history, and the other arts too. Becoming a moviebuff was often the first step on the road to becoming an arts and culture buff more generally. These days, the movies seem to lead at most to further experiences of cyber-pop culture.
Even though I'm able to enjoy stuff like 300, I'm enough of a fan of "traditional movie values" to find this trend a little depressing. And the fact that I can watch all the Fellini movies I want in the comfort of my home doesn't quite make up for this loss of a larger, serious, old-fashioned film culture.