Sooo like yea
Didn't specify what kind/which subject matter, so I'll just recommend Watchmen and Maus off the top in case you haven't read them already.
Some graphic novels I've found personally significant:
Fun Home
I Kill Giants
Blankets
Plus I'm working on one rn so I gotchu
Polar
Punisher Max
Preacher
Sandman
Y: The Last Man
Seconds, it’s by the guy who did Scott Pilgrim
Superman For All Seasons (really pretty art, not crazy comic book-y)
The Underwater Welder (kinda X-Files ish)
King City is a really awesome one. it's goofy and smart like adventure time, but also really adult at the same time.
some flavor pages:
also, everything that brian lee o'malley has made in his career
everything by frank miller
East of West
bone if you haven’t already
Sooo like yea
Jimmy corrigan: the smartest kid on earth by chris ware
invincible
So none of you motherfuckers gonna say Watchmen or what??? Read Watchmen op, its pretty good.
The Dark Knight Returns
HellBlazer
Swamp Thing
black hole
Dunk & Egg trilogy
Saga.
Flight
iykyk
we had to do assignments on 'maus' at school cant rember if it was good was to busy trying to reach 1500 words
A Contract With God
Watchmen
Spider Man: Torment
Last Knight on Earth
From Hell
Seconds, it’s by the guy who did Scott Pilgrim
Superman For All Seasons (really pretty art, not crazy comic book-y)
The Underwater Welder (kinda X-Files ish)
wow i don’t think ive ever met anyone else who likes superman for all seasons
asterios polyp
daytripper
saga
sandman
all star superman