A lot of people don't like the movie, because:
a) the monster isn't shown enough
b) there is not enough action, more guns!!!!
c) no explanations
In my opinion these are bogus reasons, because the premise of the movie doesn't allow any of these things. It's like going to a romantic costume drama (say Pride & Prejudice) and then complaining about the fact that the main characters aren't constantly having hot, sweaty sex (not the best comparison, I know).
Cloverfield is about some catastrophic event happening and depicting in a "realistic" way how a group of people is effected by this event. How realistic would it be if the main characters were constantly within stomping distance of the monster and surviving for the duration of the movie? Same goes for the action. As for the "no explanations" part, what do people want, an unknown monster is attacking New York, within a few hours the city is leveled. Nobody knows what is going on, so it should be the same with the audience. It's part of the experience that the movie is trying to create.
People should judge a movie on what it offers, not what they want it to offer (or something like that).
Rant over
Own opinion (spoilery): I liked it, it's incredibly intense and looks extraordinary. However, I didn't really care for the characters (except for Marlena, I sort of liked her). Not that I disliked them, they were just blah, disposable. It had no emotional impact when they died.
