Madrid paid Monaco €80 million for the creative midfielder, while also spending €25m to lure Toni Kroos away from Bayern Munich.
Del Piero feels the Champions League holders have strengthened well ahead of the 2014-15 campaign by bagging the duo, whom both excelled at the World Cup.
"Madrid reinforced the squad well. James is an incredible player – he’s young and has a great future ahead of him," Del Piero was quoted as saying by AS.
"And Kroos will fit in perfectly as well. He is a midfielder who will play an important role for Real Madrid."
Del Piero then went on to voice his admiration for Carlo Ancelotti, with whom he worked at Juventus between 1999 and 2001, and branded him the ultimate trainer.
"Ancelotti is the best coach of all time and I am delighted for him that he won ‘La Decima’ with Madrid. That was a special moment for him and for Real Madrid."
The 55-year-old replaced Jose Mourinho as Madrid boss in the summer of 2013 and won the Copa del Rey and Champions League in his first year in charge at the Santiago Bernabeu.