The Old Trafford side finished seventh in their first campaign without Sir Alex Ferguson and sacked David Moyes for failing to deliver European football, appointing Van Gaal as his successor.
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"Yes, he can be scary," said De Boer. "But that is because he is so passionate. He is 100 per cent all the time and he wants the same in return. You could see it on the sidelines but he could be even more intense on a Monday morning, especially if we’d lost.
"If he knew that you hadn’t played well, he would be straight on top of you. He is a big guy, he wants to win and that is where he can be intimidating and intense. But even if he shouts at you, he will listen to what you have to say.
"He gives players chances to prove themselves. If you play badly in one game he won’t drop you straight away. He will give you the trust to repay him with a better performance next time. He puts trust in players but he expects it back from them. He doesn’t want to be let down.
"He has got some great players there. He wants them to be excellent in everything they do. If you do it the way he wants he will be your best mate."
De Boer also praised Van Gaal's tactical intuition, claiming that he can see things from the touchline "before anyone else".
He added: "He would say sometimes to Marc Overmars, 'The guy you are playing against drifts across to be close to the central defender. Stay where you are and you will get in behind him,' — and he’d be right.
"It was the same with Jari Litmanen. 'Jari, the defender who is marking you sometimes thinks he is a holding midfielder also. Don’t move when he does. Let him go five yards.' Jari would do that, the chance would come and he’d score. It was like he was seeing things before anyone else.
"He is so well prepared that you would be doing drills in training and you would know what the opposition were going to do before they did. You knew exactly what you were up against."