Stop reading this and go see Cloverfield now.
I'm not kidding.
This is a fun monster movie...and the less you know, the better it is. It may be the perfect monster movie. I *really* liked it.
I got to see a special screening of this film earlier this week. The movie is like a cross between Godzilla and The Blair Witch Project...except much better than either one.
Since the movie is filmed from a video camera held by one of the characters (like Blair Witch)....expect a bumpy ride. There is a lot of running and spinning. A security guard said 16 people ran to the lobby to vomit during the movie. A friend of mine had to get up and leave because he was nauseated. All the people came back to finish watching, though. It is recommended you sit further back in the theater to lessen the impact (or closer if you want the ultimate experience!). I didn't have any problems with it, and I sat about 6 rows from the front.
Oh! And make sure you see this in a theater with good sound...it makes a huge difference! The sound is really well done (props to Skywalker Sound!) and will make you feel like you are there if you go to a good theater.
Here is the teaser (which is essentially the first 5 minutes of the movie):