In the case of "Knowing", there are indeed some truly vivid depictions of disasters complete with a few disturbing visuals of being right in the midst of it all while people are dying in quite horrible ways all aound us. That itself should be worth the price of admission, but we've seen it all before already -- in the trailer!
Ok, so the trailer does not cover every single aspect of the movie but I daresay everything I wanted to view, I could have got it off the trailer, for free. The bits that were not in the trailer, well, let's just say they didn't add much more -- except maybe a little unnecessary hokeyness -- to an already predictable plot.
There's an attempt to draw out a debate between Determinism and "sh*t happens" randomness, but it seems like a convenient placeholder for upping the philosophical ante of the movie, and it didn't sustain.
Oh well, nice concept, but not quite my cup of tea.