Iv'e said it before and i'll say it again; if any character has taken a turn for the worse since about season 10, it's Bart. And this is because he isn't much of a jerk anymore. Back during the golden age of the show, Bart was the most selfish and cynical member of the family, a role which have since passed on to Homer. Which is lame because Homer already had the role of lovable idiot. So now, Homer fills both the role of the idiot and the role of the jerk, while Bart just comes of as some character in the background whose primary role appears to be acting as Homers sidekick.