Not too bad, actually. Tony Scott's fuzzy, slow-motion thing was a bit much at the begining and I'm not the biggest Travolta fan but it was more than entertaining enough to keep me from clock-watching.
Question for someone more in the know on New York's (it was based in NY, right?) subway though; is the netweok so big that a terrorist/gangster hijack of a train wouldn't see the whole system shutdown? I found that hard to believe.