Hot fuzz. Because the first watch is enjoyable, but every subsequent rewatch makes you appreciate Edgar Wright more and more. He is just the most incredibly meticulous story teller with the most dense movies.

Memento.

Though, being real, I would say that it's a movie that gets more interesting on second watch rather than being one out need to watch twice to get. I honestly haven't ever run across a movie like that.

I like primer, but I'm not sure I really understand it even with all the charts and diagrams that are out there

Okay this isnt a movie but a show, but arrested development (especially the early seasons) are filled with situations, puns, innuendos and jokes that are set up over several episodes, sometimes even seasons. It is impossible to catch and appreciate them all on first watch. I have seen the show probably a half dozen times over the years and i still stumble over the occasional thing i missed.

Everything Everywhere All At Once.

It's just... really good.

not so much for understanding but, fight club is a different movie the second time around.

Donnie Darko. Besides being confusing, it’s just a great story. Plus, it’s remarkably well cast.

If you have the opportunity to watch the deleted scenes, I highly recommend it - especially the one with the dad. His role in the cinematic version is pretty small, but there’s a deleted scene where he has a quiet chat with Donnie, and tells Donnie about his past mental problems. It’s fantastic, and rounds out his character perfectly.

Groundhog Day. It gets better with subsequent watches.

The Big Lebowski. I've never seen another movie gain so much value over time and rewatches

The Prestige.

Snatch.

There's like 15 main characters. Every scene is important but it is impossible for it all to be apparent on a first watch.

It's really brilliant storytelling. Watching Lock To k & Two Smoking barrels, you realize that guy Ritchie might be a one trick pony. But that's okay, it's a great trick.

The Big Lebowski. You pick up on stuff with each watch, and it just gets funnier when you do.

The Sixth Sense, if you can go into it blind. I'm usually pretty good at figuring out a movie's plot twist, but this one caught me completely by surprise. Then when you watch it again you pick up on all the dropped hints.

Akira. It's weird and confusing. Goes from cyberpunk eye candy to bizarre metaphysical reality warp real quick.

Shutter island watches completely differently on the second watch, same with Primer, The usual suspects, and Moon (2009).

Primer. Gotta watch that one a dozen times and still not understand it fully.

Ghost in the Shell

Shaun of the dead has so many jokes in that its hard to catch them all. There is some good YouTube videos that also explain them in case you missed any.

Predestination. I did understand the first time but there are so many little details that I had to watch a second time, now knowing the plot, to absorb everything.

Ps: Please, don't ask what it is about. if someone explains you will lose a very cool crazy movie. just go warch it.

Primer

The matrix and Fight club ( both released in 1999 )

Triangle HORROR/BLOOD

I absolutely PROMISE you a fulfilling time, and this is a movie that could be discussed at length for a long time and still have more to say. Please don't research or you'll spoil it some, but there's more than just that. I love this move with EVANGELICAL passion.

Timecrimes on steroids.

https://www.imdb.com/title/tt1187064/

L.A. Confidential

There are multiple investigations/cases and multiple character arcs, and it all comes together so beautifully. The [REDACTED] reveal is amazing.

Edited to remove potential spoiler.

Vanilla Sky! It’s a truly mind bending movie, with an absolutely perfect soundtrack. I’ve probably seen this movie more than any other. I still find personal meaning in it 20+ years after my first watch as a kid when my older brother decided to see it in the theaters and took me along. I was confused but moved by it and I didn’t know why. Love came after the second watch.

Memento

Satohi Kon's "Paprika" is still my favourite movie, and there is a lot to discover and reflect on, on second and third and umpteenth watches.

Waking Life.

If you wrap your head around it after the 2nd viewing, you're doing better than most people.

It took me a few watchings of Akira to really have it all sink in.

Koyaanisqatsi

Visual poetry. Literally. It's conveying a message, it's just you have to come up with the dialogue. Beautiful work. The sequels are fantastic as well.