This book is uncomfortable. We are right in the head of a narcissistic personality, or at least to me Popinga felt truly narcissistic. So of course he's also an unreliable narrator. But that's exactly what makes this story fascinating and captivating. We follow Popinga, see the world through his eyes.
If you're new to Simenon, I might wouldn't start with this, but if you're interested in psychology it might be a book for you.