I find ecchi to be the hardest genre to score. almost none of them are trying to do anything but appeal to degeneracy, so to criticize them for not having a good story and character development is missing the point. but how can you use a different criteria for one genre that applies to none other?
so i pretty much just score ecchi from a 1-7 scale -
1-4 being gross of varying degrees (bad artwork, crosses a line...some of these shows will send you straight to hell)
5 not gross, but still fastforwarding through it all
6 has attractive designs, but the mc does nothing because he's a p*ssy
7 has attractive designs, MC isn't a p*ssy and does what any abled bodied male would do in his scenario (but not hentai)
a couple of anime have gotten 8-10s, usually for reasons outside of the ecchi genre. Like GTO being a ten for giving pointed commentary on issues in secondary education, both from the perspectives of students and teachers.
DxD would typically be a 6 here because Issei is gigantic p*ssy. but I'll give it a 5 because Shinmai Testament exists, and I don't know why anyone is watching DxD over that. Basara is what the ecchi viewer wants to be.