Giggs' side sealed their spot in the tournament with a win over Hungary on Tuesday.
"He came in off the back of a great manager who had huge success, and it was always going to be tough.
"But he has got us there. I think questions have been asked of everything really - selection, tactics - but nine times out of ten he has got it right.
"That is one of the big reasons we have made it. He has done the job - the ambition and target was to get to the Euros.
"Any way you get there is huge success, and I think a lot of people are going to have to eat their words."