My anime folder isn't particularly big - typically it's easy enough to find a streaming site to watch subbed anime on. I've mainly just downloaded series I want in good quality or that are otherwise not easy to find on streaming sites. Some I downloaded back in the mid-2000s before streaming sites were common. Also a fair few that were ripped from DVDs I own. Currently my downloaded folder contains:
A.li.ce
A Place Further than the Universe
Angel Beats!
Armitage III
Ben-To
Clannad
Clannad After Story
Code Geass
Cowboy Bebop
Cyber City Odeo 808
Darkside Blues
Death Note
Demon Slayer (Season 1 only)
Descendants of Darkness
Dragonball Z & GT (subbed versions, as well as many different English dubbed versions - also all of the movies)
Final Fantasy - Legend of the Crystals
Final Fantasy - Unlimited
Full Metal Alchemist
Golden Boy
Guilty Crown
Gundam Wing
.hack//Sign
Last Exile
LR - Licensed By Royalty
Love Hina
Masamune-kun no Revenge
Neon Genesis Evangelion
Origin
Ouran High School Host Club
Outlaw Star
Psycho Pass
School Rumble
Sega Hard Girls (this is not some kind of weird retro gaming hentai, for the record)
Serial Experiments Lain
Sonic the Hedgehog (OVA)
Space Pirate Mito
Steins;Gate
Steins;Gate 0
Street Fighter
Tengen Toppa Gurren Lagann
The Legend of Black Heaven
The Disappearance of Haruhi Suzumiya
The Disappearance of Nagato Yuki-chan
The Melancholy of Haruhi Suzumiya (the fucking endless eight... if you know, you know)
The Promised Neverland (Season 1 only)
Tokyo Ghoul
Trigun
Vision of Escaflowne
World of Narue
I'm yet to watch A.li.ce, A Place Further Than the Universe, Darkside Blues, Descendants of Darkness, either of the Final Fantasy animes, Last Exile, Masamune-kun no Revenge, Origin, Street Fighter or World of Narue... so still quite a few there that I need to watch.
I watched the first couple of episode of Last Exile and LR - didn't immediately grip me. Not sure if I'll come back to them. Tengen Toppa Gurren Lagann has a big reputation but I didn't find the first few episodes very entertaining and from memory I didn't like the art style much either. I should go back to it as it's really well regarded, but it's a rare anime where the art design really bothered me.
Was going to list my favourites but then realised I was including like, 70% of the list, lol. Gun to my head Clannad After Story and Steins;Gate probably hit me hardest emotionally. DBZ, Gundam Wing, Bebop, Outlaw Star, NGE, Escaflowne and Trigun all stone cold classics from the 90s/00s. Then there's the mid-00s stuff which I also love - Death Note, Code Geass, all the Haruhi Suzumiya stuff...
Well, all I can say is I feel sad for people who can't see past the 'lol weeb' or 'cartoons are for kids' mindset, because there really are so many awesome anime series out there that blow away the vapid nonsense that infests modern streaming platforms.