The biggest problem with releasing this film with the monicker "Director's Cut" is that it implies that the version released in 1979 was tampered with by the studio. This version of the film is perhaps best termed a "Special Edition," as the original edit of the film was Ridley Scott's.
I ran a search just to find out what the release date of the film is (October 29th), and was surprised to find that it is the subject of hot debate. Interestingly, this is one case where fans of the film are very much aware of what has been cut from the film because of the fact that the deleted scenes have been available for years, first on the CAV box set laserdisc, then on the initial DVD release.
I found most of the scenes that were cut to be very interesting additions to the film. I have even edited a version of the film together with these scenes a few years ago from the laserdisc (we'll see how close "my" version of the film is to Scott's on the 29th), which are mostly short bits of dialogue. It enhances the character relationships, especially between Ripley (Sigourney Weaver) and Lambert (Veronica Cartwright), who have a tension between them that is never explained in the theatrical version.
Actually, the main bone of contention seems to be about the "cocoon" sequence at the end. This is one scene I did not put into "my" version of the film owing as to the fact that it contradicts what is later seen in Aliens, and then the two other sequels. This is also the reason why so many people logging their opinions online have expressed ambivalence about the new cut of the film.
I have to say that, if one takes Alien as its own film, instead of considering it the first part of a franchise (this is difficult in today's cinematic landscape, I understand), the new version is a perfectly reasonable alternative to the original. The fact that it may not fit so perfectly in with the film series is secondary.
Alternate versions of both The Exorcist and Apocalypse Now! have been released theatrically. In both cases, I prefer the originals to the redone (or "Redux") versions, as is the case with the Star Wars trilogy. That does not alter the fact that the different interpretations are interesting. In the case of The Exorcist, the "version you've never seen" is, in fact, a take on the film that author William Peter Blatty was an advocate of, while director William Friedkin prefered a "colder" approach. I believe that Friedkin's instincts was what made the film so effective when it was released, but it was still interesting to see a different take on the same material.
Having alternate versions of films available is nothing new; Warner Brothers released an edition of The Big Sleep with both the 1945 and 1946 edits of the film so that they can be compared, Ridley Scott himself produced no less than three different theatrical versions of Blade Runner (the original, R-rated cut, the international cut [which has more violence] and a "Director's Cut" that, like Alien, implies incorrectly that the original cut wasn't Scott's).
The problem is when the new version is supposed to supplant the original. This is what George Lucas is attempting to do with his original Star Wars trilogy. In some cases, the replacement makes sense. Terry Gilliam has eliminated the slightly compromised American cut of Brazil with the European cut (albiet with the American opening), although he liked the idea of including the "Love Conquers All" perversion prepared by the studio in the Criterion edition of the laserdisc and DVD. The restoration of Spartacus includes a scene cut because it made the Hayes Commission uncomfortable, in which Crassus (Laurence Olivier) hits on Antoninus (Tony Curtis). Without this scene, Antoninus' subsequent actions seem unmotivated.
On the other hand, there is a certain amount of importance in the preservation of an original cut of a film, particularly if it is historically significant. The restoration of Touch of Evil follows more closely director Orson Welles' intentions... but the opening title sequence of the original version, with its raucous Henry Mancini music, was one of the most distinctive moments in film history. There is a certain amount of importance in showing the limitations of the special effects in the original Star Wars trilogy (and from what can be learned from how important characterization is over flashy digital effects).
I, myself, am interested in seeing the "cocoon" sequence with the rest of the film, but I also have the original version of Alien on laserdisc and DVD (it is my understanding that the upcoming Alien Quadrilogy box set will contain both the original and recut versions of the first three films). Just because it contradicts the Xenomorph life cycle in the sequels does not alter the fact that it is a very frightening sequence (and one which gives the first film a sense of closure with regards to that life cycle that it does not otherwise have). Let us not forget that in 1979, the idea of a sequel to this medium-budget film was not a certainty, and nobody knew the effect that it would have on either cinema, the horror and science-fiction genres, or Sigourney Weaver's career (which is an important one in terms of women in film).
I am, of course, very excited about seeing one of my favorite films on the big screen, but I am also interested in seeing an alternative version that would have a slightly different pace. I may well, in the end, prefer the original cut, but it will be nice to know that when I see this film in the theater that I've seen countless times (and still remains terrifying, damn it) it will have some surprises that I don't know are coming.
Because, in space, no one can hear you scream...