For me, coming out of a horrible D/s experience, it was that He was consistant.
His words and actions were in allignment... are still in allignment.

That was such a change from what I had known.

I seemed to be holding my breath, waiting for Him to hurt me or leave me or declare me unfit to be submissive to Him. I remember times in the beginning where I pushed, almost daring Him to give up and walk away. But He stayed.

I love that He is comfortable being Himself (perhaps because I am often not that way myself) and doesn't take Himself too serious. (Because I am easily too serious)
He is intelligent, creative, logical, has a way of being the eye in the storm.
And even when He is in a storm himself, He keeps me tethered to Him.
These are all the things I can actually verbalise. Lots more I can't seem to find words for right now.