I thought the plot and acting were not that great, but the execution was superb. Also, i enjoyed the concept; they didn't focus on the monster's history or appearance but let the movie pan out as though the city were really being attacked, and you are in the middle of the attack with no idea what's going on. The shaky cam didn't bother me and only bothered one of my friends a little during one of the more precarious scenes towards the end of the film.
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I feel they nailed one important aspect of an attack by a giant monster. When do you suspect the only time you'd get a clear view of the monster? Right before you die, i'd say. Also, nearly everyone that partakes in the idiotic adventure to save someone trapped across the city dies, as they should.