I've read a few VNs in Japanese that never got English translations (shovelware), and I've switched mode on a few briefly that allowed going back and forth between English and Japanese when I encountered something that struck me as odd in the English text (decent but not "great literature" moe VNs). I don't think I'd have been missing much on those if I only had English text instead.

That said, I've found a lot of hentai is so badly translated that it is worth reading it in Japanese instead if you can.