Compared are the Theatrical Version and the Alternate Version that contains an alternate ending. Both versions are available on the UK Blu-ray by Arrow Video.
Bob Carter wants to take his family to California in a trailer but he wants to make a detour to a silver mine in the middle of the desert first. He ignores the gas station attendant's warning not to go there because the area was being used for atomic tests by the army. When crossing the desert, they get in an accident and the axle breaks. Bob and his son-in-law leave to get help. Being unaware that a family degenerated by radiation is living in the hills and targeting the Carter family.
With "The Hills Have Eyes", Wes Craven created another classic with a nicely grim low budget atmosphere. Though the movie is not very bloody, the subject cannibalism and the family's transition who recognize that there is only way out still works nowadays. The original cut was supposed to be rated X which would have been a financial disaster. In order to avoid that, Craves made a few cuts and the movie was rated R.
With "The Hills Have Eyes II", a very mediocre sequel was released in 1984. However, French director Alexandra Aja made a surpringly outstanding remake in 2006. A sequel of that was released in 2007.
Fun fact: In the German audio track of the original "The Hills Have Eyes", the degenerated rednecks were aliens. Allegedly, a U.F.O. landed in the area years prior to the Carters' arrival and people have gone missing ever since.
On 10/03/2016, the Blu-ray by Arrow Video was released in the UK. For this release, the movie was restored and as the comparison on caps-a-holic shows, the Arrow release is superior to any other Blu-ray release. Besides all the bonus features (3 audio commentaries, a documentation, interviews, outtakes, alternate ending, trailer, picture galleries), there is also a booklet with 40 pages and a slipcase. For the very first time, one now has the option to watch the mvie with the alternate ending. Though said alternate ending is also available on other releases, it was always isolated as part of the bonus features. All in all, Arrow did it again and their Blu-ray is highly recommended.
In the alternate version, Katy's and Bobby's fight with Mercury follows Doug's fight with Mars. Then the surviving members of the Carter family at sundown and that is it. The Theatrical Version on the other hand ends more sinister with a shot of Doug after he kills Mars.
Theatrical Version: 89:59 min
Alternate Version: 91:18 min
Katy sees Mercury approaching the woman in the chair. She tells Bobby to start the car. With a sling, Mercury gets dragged to the car. All of a sudden, they are out of gas and Mercury manages to get free. Katy and Bobby get to the trailer. They open a gas canister and place a match behind the door. Then they get out through the window in the back. When Mercury opens the door, the trailor explodes. Bobby wants to take a closer look to make sure Mercury is actually dead but Katy is against it. When he is standing in the rubble, Mercury attacks. Katy grabs an axe and attacks Mercury while Bobby pulls his gun and shoots the guy. Mercury is lying dead on the ground.
Theatrical Version: 4:14 min
Mars longer, then Doug. The image turns red, "The End" pops up on the screen, then the end credits.
Here, Kate and Bobby handle Mercury. The last shot of it turns into a freeze frame, then a transition to the sundown. The survivors of the Carter family gather and hug. Katy approaches Ruby and grabs her hands. Then the actors one by one, followed by the end credits.
Theatrical Version: 1:27 min
Alternate Version: 7:00 min