At this point I'm reading this manga out of spite. Every time I think the plot might finally get good it proves me wrong. How disappointing is it that none of the mobs in his own dungeon recognise him? All the girls are literally useless ecchi fillers, and every single battle is "oH sTaY bAcK tHe MiGhTy DiAbLo WiLL pRoTeCt yOu". We finally get cool powerful/interesting characters in the form of the demon girls, and they immediately get cut.
I've gotten to the point that I'm skipping entire panels in this dungeon arc because without fail every sentence of "plot delivery" has to be followed by "Oh as expected of diablo-sama" "Ohhh wow that's such a powerful thing to do-ssu!"
What's most annoying is the author constantly reminding us that diablo might run out of mp but you never see the consequence, or a change in the way that he uses magic. It's like the author writes 'I'm almost out of mp" and then goes through amnesia.
If you wan't smut, read a hentai. If you want a good manga, look elsewhere. This aint it chief.