The plot build-up was very good, a hallmark of a true disaster movie. I quickly saw it as a quasi-science thriller, and it hinted all along the first three-quarters that it would be. The fearsome 'predicted future' was really great for the thriller factor, I feel. The CGI was pretty impressive as well, perhaps becoming the norm rather than the exception for most movies nowadays.
Unfortunately, aside from good plot build-up and pretty graphics, it went downhill from there. Nicolas Cage's character was not developed as well as it could have (he was mostly panicking throughout the movie), but the background they gave him was believable enough. The actor who played his son did well in my opinion, but again, could have been better.
The killer for me was the last quarter. Seriously, angels as aliens? And of all the things to save from a planet-to-be-destroyed, why rabbits? Some things just cross the thin line that separates the fantastic from the foolish. It was a real anti-climax. While the disaster-theme was done enough (the final destruction was just ubercool), a shoddy and a not-quite-makes-sense ending really brought down the value of the movie for me.
Worth watching if you are really into disaster movies, or have nothing to do.