In my opinion Prisoners, Blue Jasmine, The Assassination of Jesse James by the Coward Robert Ford, Rush, Moneyball, The Rover.

Dangerous Liasons....it is a movie that taught me the dangers of "harmless" seduction...plus, I love all of the actors and actresses in this movie...

Kiss of the Spider Woman
Raúl Julia and William Hurt

I'd have to go with a couple of underappreciated works that are generally well-regarded but not seen as much as they should be, "City of Hope" by John Sayles and "The Paper" by Ron Howard. I would consider both to be masterpieces of storytelling.

Bigfish
Peaceful Warrior
The last samurai
Hidalgo
I love so many underrated movies!

One of my favorite films is "Singing in the Rain". It's hilariously funny and the dancing is spectacular.

I'm an antipodean so...
Bad Boy Bubby
Romper Stomper
Gallipoli
Once Were Warriors
Rabbit Proof Fence
Peter Jackson's first three - Bad Taste, Meet The Feebles and Brain Dead
The Piano

A Superhero movie called :"Super" and "District 9." Both a wee bit off of the beaten path,, But must sees imho..

The footage of the last Thylacine. Link provided. It is only three mins. of your time, for something profoundly sad.

Gattaca has been my favorite movie since I first watched it.

Let’s see, underrated movies that haven’t been mentioned..

28 Days Later - In regards to zombie(ish) movies, this one is in a league of its own.

Pandorum - Sci-fi/horror/thriller with one hell of a story and the ending tops it off.

Running Scared - This movie is to Paul Walker what The Dark Knight was to Heath Ledger.

Gattaca is definitely a good choice. Gee I’m going to really ponder this question. There could be so many in different genres. Nice question and suggestion.

I loved Stardust. But also like 50 first dates, Mask, Erin Brokavitch and RHPS.

I have several, but #1 on the list is Fight Club, and #2 is Antwone Fisher. Edward Norton is one of my favorite actors, and he was amazing in Fight Club. Antwone Fisher was Denzel Washington’s directorial debut. Both movies have such deep meaning, and I have shown both movies in group settings (substance abuse treatment and sex offender treatment program), and they helped many clients drop defenses and face those deep seeded issues they have been burying for the majority of their lives. Both are excellent movies.

I thought Cabin in the Woods was amazing, but nobody I know was interested in seeing it!

Now, IF you were asking about 'over-rated' movies that'd be different since my list would begin with " Titanic" - the version with Leonardo de Crappio starring, followed a very close equal being ALL Biblical based movies and or religion based ' Life Stories/Documentaries.'
But, imo, the most under-rated movie of all time would have to " St. Helens."

I too liked Gattaca. Some others:
October Sky
Dr. Edward Jenner: The man who cured smallpox

Mystery Alaska.
Not a lot of people saw it, but it was a great feel good movie.

Fresh (I'm curious, how many people here have seen it?)
Higher Learning

If I base this on movies I watch over and over again it would be The Martian, The Boat That Rocked and Sink The Bismarck

Antonia's Line! It's a foreign flick, but I trust reading isn't an issue ?

"The Loved Ones" with Jonathan Winters, Robert Morris, and Rod Steiger. A funny movie, dark but funny.

Slap Shot

Logan

Im a huge film buff, and there is a plethora of movies that are great that don't get seen by wide audiences.

Here's a small list of films I'd recommend:
We Are Stilll Here.
Baskin
The Void
Sorry to Bother You
Interview with a Hitman
The Man From Earth
Wind River
Hell or High Water
Predestination

I have a hundreds more under appreciated gems.

Wonder Boys. Not sure if it’s underrated. It’s just not well known. One of my favorites.