I'd echo Big Lebowski and Full Metal Jacket. I'd also add Paths of glory, Eyes Wide Shut and Barry Lyndon to movies you should watch, maybe Clockwork Orange as well.

 

Fight Club

Ran

Scarface

Forest Gump

Braveheart

Monty Python and the Holy Grail

Jurassic Park

 

Update time. I've been following this without fail so far, and have watched:

Apocalypse Now: The Final Cut (4K)
Blade Runner: The Final Cut (4K)
Blade Runner 2049 (4K)
Casablanca (HD)
2001: A Space Odyssey (4K)
Taxi Driver (HD)
Alien (4K)
Aliens (HD)
Reservoir Dogs (HD)
Psycho (4K)
The Godfather (HD)
Pulp Fiction (HD)
Jaws (4K)
Arrival (4K)
Lawrence of Arabia (HD)
The Shining (4K)

Stand-out movies have been Blade Runner 2049, Casablanca, Psycho, Pulp Fiction, Arrival, and Lawrence of Arabia. But the standard in general has been very high. The only "duds" have been Taxi Driver and Aliens. I also struggled with Alien, but I managed to enjoy it for the audio and visual aspects even as I got incredibly annoyed at the characters/plot.

I've also made some adjustments to the 2021 list over the last few weeks. Essentially I've introduced a few more classic films and have taken out some which are re-watches that I included because I wanted to see in remastered/higher quality form e.g. The Matrix, Gladiator, Mean Girls. I'm still going to get those but they will fall outside of the challenge.

So the list for the remainder of 2021 is now:

The Godfather II (HD)
Rocky (HD)
Gone With the Wind (HD)
Vertigo (4K)
The Princess Bride (HD)
There Will Be Blood (HD)
Saving Private Ryan (4K)
Goodfellas (HD)
Hot Fuzz (HD)
Seven Samurai (HD)
3:10 to Yuma (2007) (4K)
American Psycho (HD)
Stagecoach (HD)
No Country for Old Men (HD)
Citizen Kane (HD)
In Bruges (HD)
Zootropolis (4K)
Mad Max Fury Road (4K)
The Usual Suspects (HD)
12 Angry Men (HD)
Inside Out (HD)
Inglorious Basterds (HD)
Total Recall (4K)
BlacKkKlansman (4K)
Fight Club (HD)
Django Unchained (HD)
The Good, the Bad, and the Ugly (HD)
Halloween (1978) (4K)
Spartacus (4K)
Se7en (HD)
Once Upon a Time in Hollywood (4K)
Bridge on the River Kwai (4K)
ET (4K)
It’s a Wonderful Life (4K)
Paddington (HD)
Paddington 2 (4K)

And because I've been enjoying it so much, I've already got an extensive shortlist for next year:

Scarface
Schindler’s List
The Big Lebowski
Jurassic Park
Close Encounters of the Third Kind
Batman Begins
The Dark Knight
The Dark Knight Rises
John Wick
John Wick 2
John Wick 3
House of Flying Daggers
Airplane!
Doctor Zhivago
Amadeus
Rear Window
Titanic
Dr Strangelove
The Breakfast Club
Monty Python Life of Brian
Gandhi
Annie Hall
Breakfast at Tiffany’s
Kill Bill Vol I
Kill Bill Vol II
Predator
Terminator
Terminator II
Hereditary
Ben-Hur
Fast Times at Ridgemont High
The Ten Commandments
Scream
Rebel Without a Cause
The Grand Budapest Hotel
Butch Cassidy and the Sundance Kid
Before Sunrise
To Kill a Mockingbird
One Flew Over the Cuckoo's Nest
Fargo
Some Like it Hot
The Verdict
Parasite
The Deer Hunter
The Maltese Falcon
For Whom the Bell Tolls
The Big Sleep
The African Queen

I might do the same thing again and move some of the 4K rewatches like John Wick out of the list to make more space for classics I haven't seen before. In particular I'd like to add a few more Westerns.

 

For Westerns, try Silverado, The Quick and the Dead, Shane, and The Magnificent Seven

 

I know it’s already in your list, but you should watch Seven Samurai before Magnificent Seven. The latter was based on the former. I liked them both but I really enjoyed Seven Samurai. It has some really interesting themes (esp. about individual/community) that are represented visually (e.g. with villagers moving around as a unit) and I think the comedy, which was unexpected, is great.

 

On the list of Westerns to watch, I'd be remiss not to recommend Clint Eastwood's final Western Unforgiven.