I am writing this review after about a month finishing the latest translated novel (15), so if I'm off on a few things I apologize. The one thing I most liked about this novel series is like what everyone else has said: it's an ecchi/harem with a PLOT. Don't see that often or at all. The main plot is enticing enough to keep reading because you want the thing in most harems, to see the MC choose, issei does but no spoilers. The side stories in volume 8 and 15 were good, seeing the backstory of the characters and how they came together were very welcomed.

Now for the review

Story 9- no story can be called perfect, but DxD is well thought out by the author, changing the view point from 3 different characters: issei, kiba and azazel. I liked that part of it because we get different perspectives of the storyline. The different plot arcs are played out very well and how fights are written are good(just want pictures for all of his different balance break armors). The current arc is about vampires and gasper(him in the anime, seeing him will question if a boner is called for because not only is he a cross-dressing androgynous male, but they drew him as close to female as possible, which is to cruel). See how this LN is going, I hope it doesn't end without issei shitfucking cap cao and possibly Michael/sirzechs team up, which if that happens, could be like a 20-25 OVA battle itself.

Art- 9, because there are few pictures in each novel, it's rated on how well drawn each is. Even without color, it's easy to imagine it coloured in your head. Student council prez as a magical girl is in every way just eye candy for the soul, it can't be helped but to be loved by all.

Character-10. With 15 novels, the main novels advance the storyline and 60% character development, while the side stories fill the other 40%, showing their dark pasts before having rias turn them into devils and fight by her side. I like how kiba is becoming more OP as he grows, getting Siegfrieds swords was a OP moment in itself, showing how strong he has become.

Enjoyment-10. This was the first LN I read, reading from volume 1 I got more story than the anime(to be expected). As I kept reading even though there were the ecchi moments, they never lasted longer than they had to. A Harem mostly has like 4-5 girls, where issei has 7 that fawn over him, and aren't afraid to do anything with him, koneko taking his lap as her territory was just to damn cute.

Overall-10. I love this series, the plot doesn't take total precedence, but it's actually the Amin focus. If you like the often ecchi moments you will DL or buy all of the volumes and enjoyably read them. I recommend this to any fan of the harem/ecchi genre.