I feel like people choose not to understand the character of Superman rather than actually giving reasons why he's not a good character. For people that are familiar with him, he is a good character if the right people have a good story for him. Up Up and Away by Geoff Johns was a good example as a way to make Superman a great character without diminshing who he is, same with Johns Braniac arc and the Legion of Superheroes arc! But that's not all, if anyone watched the newer Superman vs. the Elite movie, they illustrated why he's a good character, and its because he isn't willing to waiver on his morals of saving the world and people around him. Him being a goody to shoes doesn't hurt who he is, Spiderman and Captain America are the same way, it doesn't mean he's boring. It just means you know nothing about him and that you should maybe look into reading more on who the character is with some great storylines that show the character at his best.So to conclude, he isn't a bad character he just has bad writers who do very little to move him forward.