Honestly, I didn't come to GA under the best of circumstances. I had been writing on some smaller sites and someone on GA plagiarized my Not The Sun series and Hurricane Lamps. The admin staff handled it excellently: banned the asshole, informed me, and invited me over. I liked it here better.
I stayed because this is a site where it was easier to interact, not with only readers, but other writers as well, which was huge to me. I like to read, but also like seeing the discussion in the forums, the comments section, the reviews. I like hearing from other writers how they come up with stories, their processes, their thoughts as they craft stories, etc. It's very motivating.
I also really like the contests and anthologies. While I can't participate in every single one, the ones I have done have steered me into writing things that I normally would not have considered on my own, which is really cool as well.
This feels like a community, more than just a website to read fiction.