In manga and anime, there’s such a variety of characters and just like in any story some of these characters are great (characters like Goku, Edward Elric & L) whilst some of these characters just absolutely suck. It goes further than if the character is great or not though because some of these characters can be really deep, I’m not talking in the sense of their backstories but rather what the character represents.
A lot of characters represent different things and the story helps to bring them out; for example Yoh, the main character of the Shaman King series is an easygoing character, who more or less shows that you don’t have to take life too seriously and you don’t have to take yourself too seriously either. He wants to become the Shaman King in order to live an easy life which is pretty much a metaphor for working hard in life so that you can enjoy the fruits of your labour. The character representations (in my opinion) make a character more relatable because they might embody thoughts that you have about life; they also add another layer to the character.
Not all characters represent something (or maybe I haven’t understood what it is that they represent) and that’s definitely one thing that separates the great characters from the not so great characters. With that being said, there are still characters that aren’t really great that have been part of great stories (I’d name some but I feel that it’d come back to cause some stress). I could be very wrong about the whole character thing and they might not represent anything, in reality I might be reading into what isn’t there as many people tend to do.