Artwork.
You can fap to both BW or coloured manga, you can fap to it even if you don't understand the language. I really like a story that's good (or plausible at least) but, in hentai, it's nearly asking too much.
Censorship is a pain, and it really destroy hentai if excessive. However, a hentai can be at a language you fully understand and with an amazing story. How could you fap if the artwork is ugly as hell? You may enjoy it because of the story, but then it doesn't need to be hentai.
I mean, like I said, I like a good story very very very much, and I would be glad if the censorship law was abolished. But artwork is my top of tops.