In season three, Steve takes a tumble from Grace, and he inevitably becomes more human. After graduating high school, he's working in an ice cream shop with no plans on going to college and spending all his free time falling for his mouthy coworker Robin and solving mysteries with Dustin yet again.
In the end, the entire Hawkins crew has to come together to basically save the world, and now Steve is firmly part of this crew, even saving Nancy's life when the Flayed Billy was about to run her over with his car in the end. (It doesn't matter that Steve was drugged and probably did it on accident, the fact of the matter is that he did it.)
I love nothing more than Steve's little friendship with Dustin, and I think I can thank Dustin for bringing Steve down to a likable level. Long gone are the days of Nancy's douchebag boyfriend. He's still Steve "The Hair" Harrington, but at least now he's far less annoying.