The 29-year-old could return against Bolton on Wednesday and Donovan says he has more to offer than in his last stretch with the Blues.
"I'm more experienced and a better player than I was two years ago," he told evertonfc.com. "Before you get to the end of your career, mentally you get better and better.
"I feel I have grown a lot over the last two years. I've had a World Cup and I feel these may be the best few years of my career.
"Nothing is ever going to be the same, I'm hoping it's better but I just want to come and enjoy the experience," he added.
"There's not many players in the world that get the chance to play in the Premier League for a team like Everton.
"I'm very fortunate to have that opportunity and I just want to make the most of it."