Generally, I've only ever read manga or light novels after first watching the anime and am interested in seeing where the story goes from there. Is It Wrong To Pick Up Girls In A Dungeon? (I'll just call it DanMachi from now on) was the first time I reversed that and read the source material before seeing the anime. This review is based on the first 10 volumes.
I really don't like the title of this series. I find it very misleading. It gives the impression of a standard harem concept, but this story is anything but. Sure, it has the standard harem cliches, with a bunch of girls who all have the hots for Bell. But it never ever feels like the harem or ships or romance is driving the momentum of the story. There's always a bigger plot, and Bell's focus is always on overcoming obstacles and helping the people around him. It actually bothers me that some people might pass on these books thinking they're just boring harem fare, because there's so much more being offered here.
Simple explanation is that this story is set in a fictional world where a huge hole in the ground serves as a spawning ground for monsters (the dungeon), and adventurers flock to the city to fight these monsters, level up, gain fame and fortune, etc. It's a unique twist on a pretty standard RPG/fantasy theme. It weaves in some mythology, as gods from various cultural backgrounds have descended from the heavens to form familias (guilds, essentially) of adventurers. The story follows Bell, a teenage boy who comes to the city hoping to make his name as an adventurer. He finds a small familia and starts off on his adventure, picking up new comrades, potential love interests (although the romances never really go anywhere in this story), and new enemies along the way.
If I had written a review of the first volume, I might have given it a 7/10. Not great, but interesting enough that I picked up the second volume. The real strength of this series is that it picks up momentum as it moves forward. The early books set up the world and the characters, and as the stories progress they grow more complex and fulfilling. Too many series start with an interesting premise, but the author loses creativity or direction after a few volumes. DanMachi is the opposite - it just keeps getting better the longer the series goes on.
The author of the series has a real skill for building to an exciting climax. I don't think there's been a volume yet (save for 9, which is the first part of a two-part story that concludes in 10) where the story doesn't build to an epic scene that resolves the main conflict, and leaves the reader feeling wholly satisfied. I read a lot of these Japanese translations these days, and I always find that I rip through DanMachi faster than any other series, just due to the forward momentum in the plot - I can't wait to find out what happens next. There are other series I like more overall, but this is definitely the one I can't put down once I start it.
I don't want to get too much into plot specifics or character development or whatever, since I'm basically posting a review for 10 volumes of a series. It's kind of hard not to have some level of development over that length of time. Suffice it to say that the characters are mostly likeable and interesting, and their interactions are amusing when they need to be and serious when they need to be. The tones shift naturally and there's a bit of everything in each of the stories. There's action, adventure, humour, mystery, intrigue, camaraderie, and (mostly unrequited) romance. It's unusual for a story to blend so many different tones so seamlessly, but it works well here.
Overall, I'm giving the series a 9/10, based on the first 10 volumes. The first few volumes set the stage, handle the world-building heft, and the series just keeps picking up steam with each subsequent instalment. Epic climaxes top off each book, and new characters are introduced regularly without feeling forced or creating much bloat to the story. A great read, highly recommended.