I loved it and judging from the many forums I've read, the majority has liked it as well. Its one of those you either like it or you don't.
For those that didn't enjoy it nor didn't get entertained must have went in thinking it was a full on chaotic monster movie with a decisive ending OR got sick from the handheld style filming.
For me, it was basically a story of love and the emotions/actions of the individuals when faced with the backdrop of the monster (which could have easily be substituted for say an earthquake, tsunami, 9/11 attacks). The handheld style filming brings a unique prespective of the characters point of view and updates the boring monster genre.
The ending was great and watching this on DVD would not justify the film in which you cannot compare with the theatre screen and suspenseful sound production.