The midfielder has revealed the new manager was angry after Manchester United conceded two late goals against Roma, and feels his evident winning mentality is perfect for the club
The new manager has overseen two games in charge of United, a 7-0 win over LA Galaxy followed by a 3-2 win over Roma, a display the Dutchman described as "not good".
United were leading by three goals - two from Wayne Rooney sandwiching one from Mata - before Roma threatened to level after two late strikes and the Spain midfielder has revealed Van Gaal anger at full-time.
"After the game when we had given two goals away he was not very happy, but I think his way is that of a great manager," Mata told reporters.
"He says what he thinks and has a clear way of understanding football. We feel the manager is a great manager who has brought a strong mentality. This club's made for a winning mentality and I think he has it.
"He has had success in different countries. We are happy with him and the way he works. Everything is new but we are adapting well to his style of football.
"He is right to be demanding. As a player you want a coach like this, always demanding more and to play better and try to win the games earlier or in a different way."