Anime

Fullmetal Alchemist: Brotherhood might interest you. Thinking about interesting character studies - if you like stories with horror elements, Monster is great. Cowboy Bebop is a classic sci fi story. I was personally a big fan of Moribito: Guardian of the Spirit.

Well, you picked a hell of a show to start. A couple that I think are similar in feel to Frieren would be:

• Kino's Journey - there are two versions of this show as it had a remake done in 2013(?) I think. In any case, for somebody just starting their anime journey, you can stick to the more recent, less VHS-grainy looking version.
• Mushishi
• Violet Evergarden - I haven't personally watched this one yet, but it is brought up a lot in comparison to Frieren.

To Your Eternity and Violet Evergarden are some good anime to watch after Frieren.

I would say the closest to Frieren in both quality of the writing and animation (and even surpassing the animation by a mile) is Violet Evergarden. It's on Netflix so you probably already have access to it. It's just as emotional as Frieren and shares some of the same core concepts of the story by exploring what it means to have basic human emotions though the lens of someone who is struggling with them. I cannot recommend Violet Evergarden enough.

There's already quite a lot of good recommendations here. I'll just add another voice recommending Kino's Journey and To Your Eternity.

Also, I'd say don't expect Frieren levels of polish and awesomeness with the recommendations given, as Frieren is just a different level altogether (with lots of deserved hype).

As for my own recommendations? Let's see:

• Aria the Animation, Natural, and Origination — this is but one anime series with three seasons of varying length. Every episode is more or less self-contained, but the characters develop slowly over the span of a lot of episodes (I counted 72 for all three seasons, could be wrong though). In a way, the character growth and exploration here is more comparable to real life. The pacing might be a bit too slow for a lot of people though. and the overall tone might be a bit too sweet for some. There's some world-building here, but it's really subtle at times—with the episodes focusing instead on the everyday and sometimes, the supernatural goings-on around the city the characters live in.

• Natsume Yuujinchou [Nastume's Book of Friends] — six seasons of varying lengths. This is also mostly episodic with some character growth happening but the kind that you'd easily miss just watching the episodes. This one, however, has more supernatural themes, but also touches on how the youkai (non-human entities--to put things simply) differ from humans not only in mindset, but also in their perception of time.

• Mushishi — I haven't yet watched this one in its entirety, but this is favorably compared to Natsume Yuujinchou, and so it might hit the same notes as that one.

Spice and Wolf is an anime about a traveling merchant, i couldn't recommend it enough. Although there is a new anime of it coming out soon if you want to wait

Made in Abyss is a horror anime about kids exploring what has affectionately been called "Uncle Lovecraft's fun time murder hole"

Girls Last Tour is an anime about two girls exploring the apocalypse. The music is literally addicting, i typed the name and it's stuck in my head. You will cry.

Those all hit an exploration Itch, i recommend going to myanimelist.net to help keep track of what you might want to watch.

I've not watched shows that you mentioned yet so this might be a little out of left field. But anyway here's some top anime i'd recommend:

Hunter x Hunter (2011)

Beautiful world that gets bigger and bigger, loved watching the main character train up to a crazy level of power. Your idea of that character will change over the time you're watching, the writer does a good job at putting us in the shoes of his friends who also watch him grow.

Attack on Titan

This one is if you're looking for the type of character development that you'd find in a war movie, Innocent characters learn the gruesome horrors of their life and lose their innocence. The story of the world is well built and the lore is deep. Be warned, it pretty depressive to watch, i kinda lost hope with the characters while watching it does a good job at pulling you into the characters mindset.

Others to consider (i.e. anime starter kit): My Hero Academia | Neon Genesis Evangelion | Fullmetal Alchemist: Brotherhood | Tokyo Ghoul | Sword Art Online (S1) | Does Avatar the last airbender count?

Hello! Lots of good suggestions here already.

But I am here to shill for my favourite manga, now being adapted into an anime, Dungeon Meshi.

The first 12 episodes are on netflix and so far the execution has been stellar. I'm running a community for it here: !dungeonmeshi@ani.social

You mention the slow character build up and detailed world building of Frieren being enjoyable, and Dungeon Meshi excels at those same things. Personally I'd even dare say it keeps up the quality of that stuff, while it eventually kind falls off a bit in Frieren in favor of focusing on arcs that can feel like B-plots. That's not even a criticism, it's simply a different kind of story, and the anime hasn't gotten to that point.

Dungeon Meshi in comparison is fairly short (I currently estimate it will wrap up in 48 episodes, after a second season), but it is a deep and complex story featuring far more than one character worth focusing on, set in a world with a rich history. Its rate of publishing was a single chapter every other month, which I think resulted in a level of attention to detail few weekly published mangas can achieve.

It merely masquerades as a simple comedy/cooking story with a fantasy gimmick.

And now we are getting an anime adaptation of that masterpiece, by none other than Studio Trigger!

If you give it a chance, pay attention to the details, as it starts to set things up from episode one, that will come together only much later.

It's hard to live up to expectations after Frieren but here are some that were memorable for me:

• Fate Zero - it's a battle royal with magic, the story isn't the focus but the characters and fights are great
• Spice and Wolf - this is about a merchant's journey with an unusual companion (there is a new (re)adaptation coming next season, but the old version is also quite good)
• A Certain Scientific Railgun - a sci-fi city and it's secrets, I think it does well in the would building

Spy x Family

Land of the Lustrous

Yuru Camp

One Piece

Madoka Magica

Nichijou

A Place Further Than The Universe

Vivy

Violet Evergarden

Welcome to the NHK

Fullmetal Alchemist

I was watching Apothecary Diaries alongside Frieren so I gotta recommend that one.

Sci-fi and crime: Psycho Pass (Season 1 only)

Mushi-shi and Violet Evergarden have been recommended by others and I also highly recommend them.

Other shows which have exploration theme with character build up

• A Place Further Than The Universe

A group of four girls travelling to the Antarctica.

• Mushoku Tensei

A shut-in jobless man reincarnated into a fantasy world. Try his best to conquer his previous traumatic past in new world.

• Dr.Stone

Due to a mysterious beam, all the world population turn into stone. After thousands of year, a boy reawakens and tries to rebuild the civilization.

• Made in Abyss

Following her mother trait, a girl and her friend dive down the abyss where they will meet all sort of mysterious ceratures.

Ancient Magus' Bride has a similar kind of mood with a super old wizard and girl apprentice doing emotional side quests.

Kino's journey, Mushishi, Violet Evergarden are all excellent shows but I would add: girl's last tour

And if you have time for more: 86

Madoka Magica, Vinland Saga

Toradora!, Akame ga Kill, Spy X Family. I would recommend these.

Angel Beats for a good cry

Wolfs rain is an overlooked gem about wolves and a girl at the end of the world. It was the next project the storyboard director from evangelion went on to work on iirc, one of studio bones first projects and fantastic music by yoko kanno throughout. Every character in it both good and "bad" has a motive, has a reason for their actions, and is wonderfully fleshed out. It plays a bit with character archetypes and how they break down when they are actually real people, reminiscent of EVA. Wolf's Rain is also on my short-list of great animes that also finish well.

You will cry through. Oh yes.

Imma go watch it again

I would suggest Magical Index.

It has a pretty broad spectrum of themes and characters.

The spinoff series Scientific Railgun tells a similar story from a different perspective. That is also quite enjoyable. You can decide if you want to watch one or the other or both.

I personally highly recommend Mushoku Tensei. It has some controversial points, and I feel that during the course of the story (particularly in the LN) they were straightened out since the main character stopped identifying himself as his pre reincarnation person and fully went in as Rudeus.

The art, animation, and music are all gorgeous. The world building is there, quite in depth too. Also, the first four of the first season has some of the best intros and outros I have ever seen in 40+ years of watching anime.

I may a bit biased. 😅

Blue eye samurai was so dam good.

It's not anime but the silent voice manga was super good with good personal growth