I still think Shin-Sei-Den is my favorite H game, it's pretty old now though. It has a good mix of gameplay/H content and the animations are stellar.
I just wish it wasn't so piss easy. Even just increasing enemies' health would do. Also, having more H enemies per battle would ironically help since Aika can't act while she's getting fucked.
As is the only difficult thing about the game is figuring out where to go. I guess you could enforce restrictions on yourself by having no equipment and stuff like that, but I shouldn't have to do that.