They are firm, so they allow you to sit on your sitbones rather than the softbits.
They become customised to your butt.
They are wide enough for me, without being too wide.
When broken in, they curve up in the back.
There is some breathability.

I have Brooks on all my bicycles, and find them very comfortable. I can ride long distances ... I can ride for days ... and no discomfort.

Most of my Brooks are the men's standard B17s, but Rowan put a women's B17 onto my new-to-me mountain bike, and near the end of the ride, he asked me how the saddle was. I hadn't even noticed it. And that's a sign of a comfortable saddle.