The trailer seems to have some updated shots with clearer visuals, there is also a Muto in the Las Vegas scene.
While from all accounts it wasn't a trailer but footage (I wasn't there so I can't say definitely), the crowd certainly seems to be in awe over it. More info as we get it, below is some of what Gareth Edwards said via Zap2It.
Update: The reveal was footage of the Hawaii scenes some of what we have seen in glimpses in the trailers but there is also a reveal of Muto that we haven't and the beginning of a showdown between Godzilla and Muto. Check out the video below.
"We did think about looping the [trailer] footage for two hours," Edwards jokes of the well-received trailer for his movie. Don't worry -- there is still other footage. In it, we actually meet the monster: "Godzilla tells you who he is," says Edwards.
(Original post had trailer which was removed per Warner Bros.)