The 58-year-old was appointed in December, tasked with keeping his new side in the Eredivisie. But he has now left the club after they stayed up courtesy of the season being abandoned.
The former Crystal Palace manager told Sky Sports: "Chris Powell came with me, who was absolutely superb. And we formed a good team.
"I thought the team responded well. We definitely improved them, but results were hard to come by.
"Some of the teams were very, very good. There was a good standard there, and I think four or five of those could easily compete in the Premier League."
On his players, however, he later continued: "I experienced great professionalism in Dutch football. I don't want to give a stereotypical view of them, but they are needy in terms of wanting to know exactly what the game plan is, what their role is, that information.
"They think about the game, and possibly too much at times, and could show a bit more freedom in their play."