The film was pretty much exactly as I'd expected from all the reviews I'd read, so I don't have much in particular to add about it, except perhaps that besides the obvious 9/11 and Hurricane Katrina references, it reminded me quite strongly too of 28 Weeks Later. I suspect the release dates of the two mean that that's more likely to be a case of them both drawing on the same general zeitgeist than any actual direct influence, but still interesting.
It also gave me motion sickness, which I was expecting too on the basis of reviews and my previous experience with The Blair Witch Project. But I was prepared for that, and knew what to do about it - you just close your eyes for a bit when you feel it coming on, and listen to the soundtrack, stealing occasional glimpses at the screen if it sounds like something important is happening. So it didn't really ruin the film for me or anything - although it did mean that for the first time in cinema history, I failed to finish the popcorn I had bought.