This is easy!
Full cast of ladies. You know how in a lot of stories it is literally a man's world, with maybe two or three girls—and this happens even in things where a girl is the main character? Sailor Moon is ALL GIRLS ALL THE TIME. Not just Usagi and the other senshi—most of their villains and even most of the minor bit-part characters are ladies. It is just so unbelievably refreshing to see something that's just as all-ladies-always as the stuff I write myself.
Queer characters. It's been twenty years and you still can't find stuff as queer as this manga. Bisexual characters, lesbians, canonical genderqueer character, at least one asexual character. Reading Sailor Moon is absolutely living the representational dream, for me.
Tsukino Usagi, lazy crybaby bisexual dream girl.
Chiba Mamoru, Usagi's #1 partner, best dude, badly-dressed professional kidnappee.
Tenou Haruka, juggling sailor senshi duties with being Michiru's full-time girlfriend AND Japan's most famous racecar driver. Queerest of queers.
Aino Minako, love-and-beauty pop-star team leader, who always falls in love but will never, ever let romance come between her and her duty.
Setsuna and Michiru and Haruka all shacking up together to raise baby Hotaru.
Takeuchi Naoko's drawing style, which is a bit limited in some ways—Usagi's supposed to be chubby, but you can't tell at all—while also being one of my favorite things ever. It conveys emotion really, really well, and it's cute and funny and beautiful. So many little details.
That one time evil!Mamoru brainwashed Motoki into thinking he was his best friend because evil!Mamoru needed information, and they've been friends ever since.
Neo Queen Serenity: you can FEEL how kind and loving and strong she is, and you can tell at once that Usagi will grow to be that person, not too far in the future.
How destiny is intermingled with choice; Ace might have told Minako that it was her fate to never have love, only her duty, but the truth is this: Minako decided to hold her duty to the princess above all things. She decides every day. For all of the sailor senshi, their destiny isn't something forced upon them; it's the end result of their own choices. Given the chance, not a single one of them would turn away.
Still a lot of open spots in the meme</i>, give me more things to talk about please!