I think it depends on what you're looking for. Is it some good world building, good adult content or a great story? A good story could be something like
The Last Sovereign. However, that game has some very poor CG in my opinion. Then there are also games like
Seeds of Chaos which has great CG and also good history to. If you are more into a visual novel without combat, but quite impaction decisions then go for
Good Girl Gone Bad.
I'm not much into 3D games, so I can't comment on those.
What I will say is that a lot of adult games are quite weak on the story part. Many games go for quick content without much else to it - and sometimes they add the most ridiculous reasons for the MC to either get their way with the girl or the MC get exploited by another character. Once you've played a bunch of games you will start seeing the patterns within the various genres.
In any case, I too would like to see some games which have adult content, but which are not solely focused on that. Though, we also have to keep in mind that many of the creators are very small-scale and doesn't have the means to or is confined by their engine to create deeper games.