I am a great fan of Nicholas Cage's work but I must honestly say that this movie will remain a scar on his acting portfolio.
The film started off very suspenseful and mysterious. The idea was creepy, the evidence more so, the acting not too bad I guess (although it does deteriorate) and the story line was original and creative. However, as soon as the movie turned sci-fi I lost the plot... it should have remained a thriller or an action. I would have given it an 8 or so if the final disaster was a nuclear war, if Cage prevented a large terrorist attack or something along those lines. However, the introduction of 'aliens' and 'angels' completely ruined the entire movie.
Knowing was filled with pointless scenes, poor acting and unnecessary symbolism (seriously, wtf was with the stones. I know they are biblically relevant, but you can not expect the greater audience to understand this). I think the director was a bit confused whether he should make the movie a thriller/horror, action, drama or sci-fi; so he decided on all of the above!
The only thing that redeems it is the CGI and the few moments of great suspense early in the movie.