Goblin Slayer is a very mixed bag. It is a “love it or hate it” series for the majority of readers out there. The range of reactions to the series mainly seems to do with audience expectations. If you are looking for something that is critical and serious with top-notch world building and character development, this is not necessarily for you. If you are looking for a combination of dark humor/shock value and humor, this can be a just-for-fun story. There are good and bad things about the book and how those factors rank, or whether you consider them good/bad yourself, will determine if this is a book for you.
Starting with the good, Goblin Slayer takes place in a genuine fantasy land. This is not a “trapped in a video game” scenario. By this point, everyone knows we have enough of those. The world here seems to run on D&D-type rules, with adventurers slaying monsters but not being too overpowered. People take quests, magic has limited uses per day, and so on. The other key takeaway is that this is not a “save the world” story. The stakes are rarely high, but they are personal. Goblin Slayer (the character) is driven by an unquenchable thirst for vengeance, not a sense of righteousness.
Now, for the bad bits. None of the characters have actual names. Everyone is referred to by whatever their role is. “Goblin Slayer”, “Priestess”, “Guild Girl”, etc. And their personalities pretty much match stereotypical fantasy roles for whatever character class they use. The other glaring issue is the writing. Saying the writing is bad is a bit of a stretch, but the author is no seasoned professional. It is a very basic style. If your interests lie in great works of literature, look elsewhere.
SMALL SPOILER BELOW
So, the last thing that must be addressed could be considered either good or bad. This one is really a matter of personal preference. And that is the extreme level of violence. Having watched the anime first, I knew what was coming in the book. The violence is not quite on the level of absolute extremes like Higurashi or Elfen Lied, but it comes close. It is dark, it is brutal, and it comes completely out of left field after the soft introduction. Some people are disgusted by it but for others that is the draw of Goblin Slayer. The decision there is up to you.