Van Gaal left for Manchester United after guiding Oranje to a third-place finish at the World Cup, and Galatasaray star Sneijder has explained how things have changed under Hiddink.
Sneijder told De Volkskrant: "I only knew Guus Hiddink as a person. The first impression is as I expected - things are more relaxed under him.
"Under Van Gaal, the atmosphere at the World Cup was perfect, though. Now, if there is laughter, it's a little bit louder.
"There is also room for relaxation but [Hiddink] is very clear and accepts no slacking."
Netherlands play the Czech Republic this evening.