Monster, Fullmetal Alchemist: Brotherhood Recommendations
Both are gorgeous, wonderfully faithful adaptations of their respective manga and are roughly the same length. Human experimentation, fugitives, a mastermind antagonist with a big plan who manipulates those around him, characters seeking revenge, monstrous characters (physically and mentally), a large cast that is continually interconnected throughout the show, deep mysteries being slowly unraveled, and the list goes on.
Both animes have some protagonists who undertake a long journey: they visit numerous locations, do research and meet a large cast of characters with their own story ... in order to fulfill a mission.
Both works refer to existential questions of the famous philosopher Friedrich Nietzsche:
The most famous theories: "GOD IS DEAD" and the "ÜBERMENSCH (SUPERMAN)".
They both have some similar soundtrack.
Listen: "Envy Revealed" (FMA-B) and "The Seeds of Time" (Monster).
In both OSTs there are drums that sound like a 'military march' or that allude to the 'footsteps of a monster'.
Have a large cast, have great villains, has important messages/themes, and has a large setting.
Both have main character trying to overcome an obstacle!
Lots of digging and unfolding, tons of twists, great character development.
Both start out slow but will build up. Watching these felt like seeing a huge jigsaw puzzle gradually being assembled into a bigger picture. All the different elements being introduced in both stories serve a purpose individually and also when combining them together as the stories go on. When it comes to pure composition, I always think of these two (with Attack on Titan and few others) but bottom line, these two anime are among of the best.
While they tackle different audiences, i say they are both fantastic in their narratives and characters.
FMAB and Monster also have extensive lore and history (monster set in the 80s and the lore of germany) while FMAB has immense lore and a great narrative that ties it all together. Both have fantastic antagonists and deuteragonists (grimmer, truth, father, roy mustang, lunge etc). Both protaganists go through hard decisions and have to be forced to make decisions. Both can be interpreted to be a 'hyporcrite'. Great writing in both and great uses of religious symbolism are present in both.
Great OSTs and music for both as well