Ruud van Nistelrooy struck both of Real's goals in the 3-2 defeat and Schuster said: "It has been demanding game as a title is at stake, this was no summer friendly.
"We saw a good meeting between the two teams. Of course, not everything worked out and there are many aspects to improve.
"Valencia are looking good under Unai Emery. They're the same players as last season, but are now forming a good team. The van is back on the road.
"I did not like our defending, we should be smarter. Though, at 2-1 down, the way we came back was similar to last season. We will be better at the Bernabeu."