NOT GREAT, BUT PRETTY GOOD
When I heard this was an all hand-held camera thing, I thought "Well, it's been long enough since "Blair Witch Project" that something like this should seem novel once again." However, whereas the "Blair Witch" film had a lot of shaky up-and-down camera shots, "Cloverfield"'s camera doesn't jiggle nearly as much when the camera guy is running, which is a relief. The motion consisted more of fast sweeps and jarring shots, like when the camera was dropped. It wasn't nearly as nausea-inducing for me as "Blair Witch", so if you haven't gone to see "Cloverfield" because you tend to succumb to motion sickness, just take some Dramamine or something similar first and you will probably be o.k.
The story is very basic. The special effects are good. It is a fairly fast, noisy film. I would give it three out of four stars except that I didn't like the ending, so I'll go with a two and three-quarters out of four.