The Japanese international arrived at the San Siro in January from CSKA Moscow and at first struggled to find his best form.
He has since become an important part of the setup at the club and has scored three goals in their opening four league matches.
"I have always considered Keisuke very strong," Galliani told the Gazzetta dello Sport. "The information that [Alberto] Zaccheroni gave us was really correct.
"He's an important player who dreamt of Milan and one who Milan had tried to bring here also six months before he arrived. He's a player of great class. The secret of his rebirth? The holidays.
"Six months ago, Keisuke arrived during a very busy period. He never had a chance to take a break. Russia, Milan and Japan - and all without ever taking a breath. This time, although he didn't have much time off after the World Cup, Honda was granted some days of relaxation, and now you're seeing the results. I always thought that he would score a lot."
Milan are next in action when they visit Cesena on Sunday.