I blame it on The Simpsons going into summer reruns.
I spent my senior year of high school teasing my best friend a little for getting caught up in Sailor Moon, so I must have been pretty bored the next summer: I watched The Simpsons in the afternoon, and started flipping over to Sailor Moon during the commercial breaks.
When The Simpsons went into reruns, I started watching Sailor Moon instead.
And then one day, when I wasn't going to be home, I found myself setting the VCR. (Yes, this was a while ago--Sailor Moon was in reruns on Canadian TV by then, but this was back when only the first 65-episode dub run had been released.) So I don't remember at what point I actually started following the series, but I do know that the first episode I taped was Sailor Venus' first appearance, and that that's how I figured out I was hooked.
Sorry for the teasing, best friend.
From there, it was a slippery slope. My family had only had an internet connection for a little while at that point, but it didn't take long to find out about the Japanese version of the anime (and become a sub snob, although I still think most of the original dub cast were good actors working under a lot of restrictions), discover online fandom, and, after a while, start writing fanfiction. I went to the local anime/manga club and got VHS fansubs through some friends of my brother's, and began lurking a lot on alt.fan.sailor-moon.
There were plenty of places online to discuss the series and post fanfiction (mailing lists, personal websites, ASMR and the other fic archives that pre-dated it), but afs-m was where I spent my time, and it seemed like everyone passed through there at least occasionally. The fandom was concentrated enough that I think most people knew each other's names (or at least knew the names of the people who posted a lot; as I said, I lurked a fair bit). I talked to a few people in my first couple of years in the fandom, but there are people I've never exchanged words with whose names I remember, who I have strong opinions on, whose opinions (circa 1997-2000) I know.
That isn't why I say that Sailor Moon changed my life, though. And it really did, in a few different ways.
First, it was the first series that made me write fanfiction and post it online. I was never prolific, but I got a fair bit of very positive feedback, often from people whose work I respected, and from there I became interested in the concept of fanfiction. I still write it for other fandoms (although still infrequently), but I've also become pretty passionate about the idea that fanfiction is the natural successor of the western oral and literary traditions.
Second, Sailor Moon got me hooked on anime and manga. I'm still a serious fan of both, and these days I do some freelance work in the manga industry.
Third, and probably the most significant, my circle of friends would be completely different now if I hadn't gotten up the nerve to email Greenbeans and talk to her about her (extremely popular) fanfic. Beans sent back a friendly reply, and later on, when I was taking advantage of my professors' willingness to let me do strange, geeky things as part of my coursework, she agreed to look over a Haruka/Michiru script I wrote as an exercise for a playwriting class.
From there we became friends, and she introduced me to a lot of the other well-known writers in the fandom. In the long run, this meant that I went to a con to meet up with them, and from there wound up in a different social circle that still includes some of my closest friends (the cast of His Lordship Chaos' "Curse of the Fanboys!" series), and resulted in my living halfway across the country for a couple of years. Add in the three or four other very close friends I've met through the fandom, and the fact that, ten years later, some of the other old-school Sailor Moon fic authors are still people I consider good friends, and I think we can agree that "changed my life" is a fair assessment.
So that's my story, and that's the main reason why, even though I've long since drifted out of the fandom, I still have a huge soft spot for Sailor Moon.
But it's not the only reason. Sailor Moon was a cultural phenomenon at the time, and it really brought anime into the public eye in North America. Sure, not everyone was into the notion of magical girls in short-skirted sailor uniforms, but most people knew what it was. And for the people who loved it, it was an incredible fandom to be part of.
For a fanfic writer, it was a huge sandbox just waiting to be played in: three distinct eras (two of which aren't exactly fleshed out, leaving you a lot of room!), five seasons that have enough filler episodes that you don't feel too weird adding 'filler' of your own, a big cast of interesting characters, time travel and alternate futures...it was great. And there were tons of prolific writers doing a bunch of diverse work, teaming up to do things together, sharing ideas and theories, really supporting each other. I'm still incredibly happy that I was able to be friends with so many of them, whether or not that friendship has outlasted the fandom involvement, and that they were so accepting and generally awesome. The fandom wasn't perfect--none of them are--but when I think back, that's what I remember.