Cloverfield is 
really the kind of film you should see without knowing anything about it. I'll try not to give too much away in this review, but I will write about certain aspects of the film that you may not wish to read right now. All I will say in the first paragraph is that Cloverfield concerns a group of twenty somethings in New York who are trying to survive a natural disaster, and that the film is put together in a rather unique and interesting way. Also, that it is very short but exciting. One of the better movies I have seen in quite a while, in fact.
But enough of that - if you have already seen Cloverfield, or don't really care then read on. Otherwise, get thee to a theatre.
Although Cloverfield obviously has quite a budget behind it, it probably started life as someone's experimental student film. The film stands apart from others in two ways, the most obvious being the "false document" framing device - the film purports to be the unedited camcorder footage recorded during the events of the evening, starting with the party that all the characters are attending and continuing to document the mayhem that breaks out later. I was particularly impressed with the way the film occasionally works a flashback into the plot by having the character holding the camera sometimes stop recording, accidentally revealing some illuminating seconds of what was previously on the tape.
The second bit of cleverness is that the disaster (I am intentionally being vague about the nature of the problem, but in many ways it doesn't matter) deliberately takes a back seat. Because of the framing device, the audience only rarely gets much of a picture of what is happening in the rest of the city. The film never cuts away to show the army being ordered in to control the situation, we see the army there when the characters stumble upon their operation. It also means that the audience never learns much about what is actually going on, since the characters are pretty much in the dark as well.
A cynic would say that making the whole movie from the first person perspective frees scriptwriter from having to think up explanations for some of the events (being vague again), but Cloverfield is the sort of film you experience rather than think about.
Cloverfield is interesting for one other reason - it is pretty much a retelling of the September 11th attack of the World Trade Center. The shaky camerawork, falling skyscrapers and sense of despair as people rush around through dust-filled streets not knowing what the hell is going on as part of their world collapses are all very reminiscent of the constantly playing footage from that awful day. This may strike some people as tasteless, but I am prepared to give Cloverfield a break. For one, it was 6 years ago and several worse movies about that day have already been released. Additionally, Japan has churned out countless movies that are allegories on how much it sucks to have nuclear bombs dropped on you (some notable examples are very close thematically to Cloverfield - vagueness strikes again!) so there is at least historical precedent in this area.
Cloverfield is a short movie - it isn't even 90 minutes long. This is pretty unusual in this day of 3 hour block busters, but a short movie works here where a longer one would be bogged down. Since nobody knows exactly what is happening, there is almost no exposition to impart, so the script has time to show how the different characters react and the complex interrelationships that arise in times of stress. The acting is great, with a very natural style appropriate to the story.
All in all, Cloverfield is a pretty solid little film. Highly recommended if you like this sort of thing (but ideally you won't know what sort of thing it is beforehand).