Insultingly stupid
Literally at every turn they have whatever they need to happen, happen. From the beginning where a truck somehow drives down a long line of stopped cars, to him, having absolutely no idea what is going on, start counting in his head when he sees someone getting bit (why would he do that? he has no idea it would act that fast or even wtf was going on), to him being able to get a vehicle and drive out with his kids while thousands are stuck in traffic.
The kid somehow getting out of the apartment and showing up in the nick of time to save Pitt, helicopter arriving just in time, the telephone call from his wife at just the wrong time etc, etc. The "nick of time" thing is a lot more effective when it isn't happening every other scene.
Sure there were some good scenes and I like the genre, but he's some super investigator? guy slips and blows his head off? the z's wait until the plane is about to land to show up? the plane crashes and they are the only two too survive? Really? They happen to crash close enough to walk to the facility they were going to? From extremely brief observations he's able to figure out that terminally ill people are "off the radar" off the infected (which of course is another idiotic plot point).
There are so many more examples of each, and each time it takes you out of the movie with how stupid what just happened was. IMO would have been much better if they didnt have him jet setting around the world with his hippy haircut.