You can watch the full film online at veoh, but you have to download their player. [It's gone as of 2/17/2010.] It does seem to be in pieces at youtube. Part 1 is here:
The other segments are linked from here.
Here's a trailer:
The New York Times says the London audience was not favorably impressed:
it is not so grossly exaggerated as many of us had feared, and is, in a general sense, not offensive. But as a work of art it is a complete failure, because it is anaemic and because it shows us a Christ who, though obviously a virtuous and mild man, is completely lacking in the fire and spiritual vigor that go to the making of the great leaders of mankind.
DecentFilms.com closes its review with this:
In a genre that deserves the best that artists can offer but is too often plagued by mediocrity, DeMille’s flawed but powerful The King of Kings remains one of Hollywood’s most remarkable achievements.
ImagesJournal says it "gives us a deeply reverent portrait of Jesus Christ". Bright Lights Film Journal has an extensive examination of the film. Criterion Confessions has a blog post. Bible Films Blog has a scene guide. Christianity Today has a review.