As was obvious to everyone from its opening day onwards, the 2005 "War of the Worlds" is a response to the terrorist attacks of September 11, 2001. Al-Qaeda, as the cliche yet accurate observation goes, turned Hollywood action movies into reality by toppling the towers, and Spielberg, for whatever reason, decided to respond by turning that reality back into a Hollywood movie.
Maybe he wanted to make an emotional time capsule of the experience that future audiences could access without getting bogged down in the historical/political ramifications of the attacks themselves (as pointless an exercise as that might well be). Maybe it was only his self-therapy distributed on a mass-media scale. Maybe he didn't have anything else to do and thought it'd be an easy paycheck gig to cook up with his favorite Operating Thetan buddy. Who knows? As a movie, it sucks, but as an emotional depiction of 9/11, with all the confusion and iffy continuity we experienced on that day, it's pretty effective - until Cruise and his daughter get into the cellar, that is, whereupon it becomes total hackwork without purpose or poetry.
The movie should probably have ended with Cruise's son's presumptive death by fire. Had it done so, all the shoddy plot holes and generally nonsensical details and sequences could have been ascribed to purposeful authorial subtlety - the old "unreliable narrator" trick. But there's simply nothing to be made of Cruise's grenade-powered adventure ride... unless, I guess, you count that as Spielby's "America, F*** YEAH!" moment, which in the context of a 9/11 reflection becomes even more juvenile than usual.