Tangentially related, any comic character can be made interesting, but good comic characters are ones written interestingly in the hands of multiple people (which has been a big problem lately).
In the case of John Stewart it's pretty tricky. The character was created as "Angry Black Man who teaches white guys about racism" and didn't have a whole lot else going for him. In truth about as interesting as Silver Age Hal Jordan. Once they removed that aspect of the character he became ... bland. and not in the way that every character was. Everything that was written to define his character served to make him the mild, level headed, precise character that the other Lanterns (and let's be honest, the starring Lanterns) got to play off of. Have you ever gamed with a power gamer who is terrified of doing anything that might be even remotely
interesting non-optimal? John Stewart is kind of like that. Mind you this is not a lack of character development, that is his development. There's a reason he was a completely different character on Justice League and JLU. A character they keep trying to turn comic John Stewart into, which doesn't stick do to its forced nature. When DC swapped Kyle for John on JLA they tried this as an instant change. The result is Stewart lecturing the "rookie" Flash (Well established at this point that he had been fighting crime and saving the world at age 10. John got his ring already into his adulthood) on Justice League Regulations. Recently they've been retconning in a career in the Marines prior to becoming an architect and GL. This done by making him a reservist while in college, allowing him to all of a sudden remember that he was a Marine 1 weekend a month, 2 weeks a year and can thus act like a jarhead stereotype, and slowly expanding that to "elite military sniper." Recently in the books they've turned him into a killer of planets, BECAUSE HE DOES WHAT IT TAKES KYLE!
Bottom line John Stewart is a supporting character that doesn't work when attempts are made to turn him into the starring role.