Most mysteries have a lot of characters with little to no depth. The characters are generic and meant to fill a specific purpose for the mystery which can make it plain. Holmes is different as both he and Watson have depth and interesting personalities that are independent of the mystery but also affect it.
Well, I don't know if Berserk is a "literary" masterpiece, but it's definitely a masterpiece. I'm only stating so because the medium is very different and story telling via comic/pictures is very different from writing words. The saying "a picture is worth a thousand words," kind of applies.