He had more success than people realize. The feelings about his term, coupled with the way Reagan's optimism told the tale of the terms after cloud things up a bit.
Jimmy Carter helped bring Egypt and Israel to peace; pretty hard to overstate how important that was then and now. While Nixon may have went to China, Carter gave them formal diplomatic recognition.
Domestically, he pushed deregulation in the oil, airline, and transportation industries. Yeah, a Democrat removing regulation. He also appointed Paul Volker as Chairman of the Fed, knowing full well the plans Volker had were likely to feel draconian, and his presidency would suffer just as badly. That and the "malaise" speech are a moral courage we just don't get anymore in our politicians.
His life before and after the Presidency were pretty impactful too. I'm grateful for the service he gave throughout his life.