Best experience so far might be with an RPer I've bee RPing with over a year now, I think. Funny thing is that the RP has been mostly plot. We RP on Discord now, but we met here.
I've had some incredible collaborative storytelling experiences on BlueMoon. There's been a bit of overlap with the "sister" site of Elliquiy for me because I originated there about 13 years ago.
The first one that comes to mind:
In a post-apocalyptic future two unlikely characters found themselves thrust together to weather the vicissitudes of fate. After a tenuous truce and escalating stakes they began to trust and bond and eventually found companionship in one and other. Weathering the storms and enduring hardship created a foundation of friendship that blossomed into passion and then love. And then we FUCKED IT ALL UP and threw a crazy monkey wrench into the mix that tore the lovers apart. The characters' relationship changed irrevocably and they went separate ways to recuperate and heal and find solace. And eventually they reunited and found it in their hearts to transcend the past and reignite that companionship and rekindle the bond and ride off into the sunset happily ever-after.
It could have very easily ended on a bad note but my partner and I were kinda sappy and totally feeling the wistful and happy ending. LOL! It took us about two years to tell that story but it was fuckin' AWESOME!!!