It took me a while of using DDG before I realized how much I had equated "good" with "looks like Google".
What finally hit me, hard, was that I switched the DDG theme to a color scheme designed to look like Google search results, and all of a sudden the results "felt better". Markedly better.
So, I started regularly comparing results, every time I found something that I felt I didn't get the results I expected for. I would search, and then search again with !g. And almost every time I ran into something that I didn't like the DDG results for, the Google results weren't actually any better. (The rare times they were, I reported that, and often it got fixed.)