Not necesarily grimdark or dark fantasy (some might be epic fantasy or military fantasy and so on), but with darker undertones, grey characters and serious, mature writing and story. No YA here, full adults readers only!
#2 of 12 in The Elric Saga
1976 • 66 Readers • 352 pages • 3.6
#1 of 5 in The Book of the New Sun
1980 • 426 Readers • 276 pages • 3.6
2 Readers • 5
#1 of 3 in Manifest Delusions
2015 • 117 Readers • 495 pages • 3.8
2021 • 16 Readers • 394 pages • 4
#1 of 7 in A Song of Ice and Fire
1996 • 2,714 Readers • 819 pages • 4.4
2009 • 8 Readers • 406 pages • 3.8
#1 of 10 in The Chronicles of the Black Company
1984 • 265 Readers • 320 pages • 3.6
#1 of 1 in Strange & Norrell
2004 • 1,050 Readers • 1,028 pages • 4
#1 of 3 in A Land Fit for Heroes
2008 • 132 Readers • 450 pages • 3.7
#1 of 3 in The Kingkiller Chronicle
1 • 2,263 Readers • 669 pages • 4.4
8 Readers • 4.3
#1 of 4 in The Masquerade
2015 • 422 Readers • 400 pages • 3.8
2019 • 41 Readers • 432 pages • 3.2
#1 of 7 in Gentleman Bastard
2006 • 1,575 Readers • 745 pages • 4.3
#1 of 3 in Bloodsounder's Arc
2012 • 27 Readers • 220 pages • 3
6 Readers • 5
2018 • 2,347 Readers • 409 pages • 4.3
2013 • 16 Readers • 4
#1 of 3 in The Prince of Nothing
2003 • 241 Readers • 657 pages • 3.7
#1 of 5 in Chronicle of the Unhewn Throne
2014 • 290 Readers • 493 pages • 4
#1 of 3 in The Black Iron Legacy
2019 • 140 Readers • 544 pages • 3.7
2018 • 22 Readers • 480 pages • 4.3
#1 of 6 in The Riyria Revelations
2011 • 483 Readers • 704 pages • 4
2015 • 605 Readers • 390 pages • 4
#1 of 2 in The Vanguard Chronicles
2020 • 17 Readers • 356 pages • 4
#1 of 3 in The Chronicles of Thomas Covenant the Unbeliever
1977 • 229 Readers • 369 pages • 3.2
#1 of 3 in The Five Warrior Angels
2016 • 161 Readers • 800 pages • 4
2018 • 3 Readers • 429 pages • 3
2021 • 19 Readers • 512 pages • 4