It's a manga that's been running for 20+ years now, and it's pretty incredible. One of the things that's most interesting about it, is that the author has basically reinvented himself in his style several times throughout the series, while still keeping it true to its roots. During the first 10 volumes (referred to collectively as the "Golden Age" arc), it's basically gritty 80s style manga of purely dark medieval warfare, becoming borderlined historical fiction. but in volumes 11-12+ literally hell opens up and pours itself onto earth evil dead style but in a completely serious manner. Over the next ~5 volumes you have every bit of bad in his world corrupted and risen to full blown demonic rape-fests; corrupt priests burning everyone at the stake, packs of roving goblins kidnapping women, raping and impregnating them to make more monsters, an evil god-emporer who tries to take over the world etc. It then turns into a traditional swords/sorcery fantasy where Guts assembles a team of rag-tag heroes to destroy the five God Hands of hell, one of whom was his best friend and rival during the Golden Age.