OVERALL: R1 - Region 1 allows you to listen to the audio commentary with either version of the film, but on the regions 2/4, the tracks are available only on: "Theatrical Release" of "Alien", "Special Edition" of "Aliens", "Theatrical Release" of "Alien 3", and "Theatrical Release" of "Alien: Resurrection". Further more, on the Region 1 discs, you can view an optional "deleted footage" marker, and you´re also able to view the "deleted footage" from the theatrical cut's "Supplements menu". Both of these options are missing from the Region 2/4 discs. R2/R4 are also missing the DVD-ROM feature "Interactive Script" (script to screen comparisons), and the text introduction to Special Edition of the "Alien3" . Both cover and menu designs differ slightly between the region 1 and region 2/4 discs.
General notes:
These following extra-features ARE missing from all of "The Alien Quadrilogy" -box sets (these are in "The Alien Legacy" box set):
-Original audio commentary track by Ridley Scott (from "Alien") (new commentary with the director has been recorded)
-Jerry Goldsmith's isolated score (from "Alien")
-The alternate music and production audio track (from "Alien")
-The alien life-cycle and Nostromo crew bios (2 "easter eggs" from "Alien")
-"Making of" -featurette (from "Alien3")
-"Making of" -featurette (from "Alien: Resurrection")
-"The Alien Legacy" -documentary (from the "bonus disc")
++AMC's "The Alien Saga" (This wasn´t on the previous box set, but it´s currently available on R1 DVD from "Image Entertainment"). Note, that the "Interview with James Cameron" (from "Aliens") IS on "The Alien Quadrilogy" -box set, and can be found under the "Aliens: laserdisc archive" (divided in 2 parts).