OK - to clarify: the bad parts are the basement sequences with Tim Robbins, the Jurassic Park ripoff, and showing of the creatures. Plus the characters and story (ending especially) are thin foils for the spectacle and detail. This is less a 3 act character journey and more a horror show, and at the end, you are THANKFUL it ended so abruptly.
BUT - the first hour IS amazing. The score and effects are superlative. Cruise and Fanning are excellent and portray the bludgeoning terror perfectly. The intensity and emotional impact are ridiculously absolute, and highlighted with horrific and macabre detail that harkens back to 9/11: the burning train, the desperation, the picture board, the looting of the car, the bodies in the river, the ash, the clothes, desaturated colour...how the hell did this get a PG-13 again?
Plus, the choice to focus on the family instead of the destruction was wise, and makes us feel the psychological unease...The moments that always leave me breathless...Cruise wiping the ash off his face, his life changed in 10 minutes...the bridge collapse... when Rachel turns around before getting on the ferry, watching the trees move...and Ray looking out helpless over the 'red weed' that has snaked over the landscape... a truly devastating and awful image that has a cold alien beauty,
and the knowledge that the red weed is the harvested organic sludge of a humanity that is helpless to resist such utter devastation is very unsettling to say the LEAST. One of Spielberg's best, I feel.