The previous reviewer criticised Knowing for being illogical and for having "some bits that are just downright dumb." I couldn't disagree more. The plot of Knowing makes perfect sense, but you need to approach it (or at least understand it) from a specific perspective.
Imagine for a moment that the basic ideas in the Bible are true: that the world was created by a powerful God, that angels exist, and that the events in Revelation are essentially correct. Now imagine that what we have in the Bible has been romanticised, that what the various writers in the Bible called "angels" aren't quite angels; that Ezekiel's "wheels within wheels" are technological rather than spiritual; that the rapture doesn't involve the rescue of believers but the rescue of the innocent.
Now, take those ideas and create a film around it, and you've got Knowing. If you can identify and recognise the various Christian elements in the film and understand how they fit together, particularly from a non-Christian perspective, you'll see that the story isn't illogical or "dumb," but perfectly sensible and certainly more credible than the plots of other disaster movies out there.
Knowing is a fascinating movie that's well worth your time, even for the judicious use of computer-generated visuals or the ending. It's an epic story that takes us from a very shallow perspective to a grander scale in the span of two hours -- and there's no other film I've seen that's like it. No, it's not The Godfather, but again, it's certainly worth your time.