There's been more hype leading up to the release of Cloverfield than any other movie in memory. There's been a ton of viral marketing, and while I haven't followed all the ARGs and all the trailer analyses out there, I have heard good things about the movie, and was very much looking forward to seeing it, which Linda and I did last night.
I won't say anything to spoil the movie, but easily the closest movie comparison I can make is The Blair Witch Project, as they're both very much in the same style: cinéma vérité via shaky-cam. The camera was at times annoying, and I can see it giving people motion sickness. And although I enjoyed the movie, I can't see myself re-watching it.
There were definitely tense moments in the movie - presenting things from the characters' point of view really immerses you in the action. But similarly, since the characters never know what's going on, neither do you as the viewer. My biggest complaint is that we never see the movie's plot resolved. I'd have liked some kind of epilogue, some more solid conclusion.
The monster isn't exactly what I imagine anyone expected, and I don't think it's a spoiler to say that it isn't Godzilla or Cthulhu. Neither is this a disguised Voltron or Power Rangers movie. It channels Alien and I Am Legend at times, and has at least one of those ECU Blair Witch "I'm so scared" moments.
If you're into going out to the theater, I'd recommend Cloverfield, as that kind of Godzilla-esque experience is certainly better on the big screen than it would be on your TV at home, but it's not going to be my movie of the year.