Pleasantly surprising, since its from the guy who 'did' Lost. Personally, I expected it to be an Unanswerable Questions-fest, but was pretty shocked to see how vividly the creatures were shown.
I loved it though. Americans can't do realistic horror situations half as well as we do (see: first half of 28 Days Later). It was very clearly influenced by the footage people got of 9/11 though. The shop scene at the start was almost an exact recount of the footage of the New Yorkers taking cover from the collapsing WTC.
It was made on subtleties that really hit you hard. For instance, the bits of news footage you saw, but more than anything, the horse pulling the carriage.
I also watched Bullitt and it was WELL GOOD. Steve McQueen's clothes were SAFE.