Gekka Bijin

Both are older BDSM hentai where the MC, a guy new to BDSM, gets to dominate an already 'trained' MILF after her previous partner is out of the picture. How this happens and the way the plot develops is vastly different in each case, but both are almost exclusively BDSM. In Gekka Bijin this is consensual and more positive, while in Hana Dorei it is more egotistic and negative. All in all, despite having nigh opposite characters and themes, they show off the BDSM well. 

Although different in many aspects, both series share a common theme in consensual BDSM, not something I have seen much of, especially compared to the nonconsensual kind. Other than that, however, they are rather different; while Maid in Heaven shows us a considerably wide variety of BDSM practices from the girl's point of view, Gekka Bijin foregoes most of these, sometimes grazing the surface, and instead presents us with a large treat of bondage (in all kinds of poses) sprinkled with a bit of plot, several girls and a yuri scene as the dessert. As an added bonus, they are both good ol' uncensored hentai.