Saw it this morning at IMAX Bradford. This is a must see 3D movie. The experience was so good my wife actually had motion sickness at the end (though she recovered enough for curry at the Kashmir).
The 3D is totally immersive, it feels like you are there on set. In fact its so realistic that you occaisionally take it for granted and then have to pinch yourself that you are watching a movie.
To anyone who can get there I reccomend IMAX, it cost us £24 for a family of four, thats actually cheaper than cineworld on a poxy small screen.
Casting of Sigourney was inspired choice!