My guess is that "The Sandman" is the best comic yet created. I've been super excited to see it adapted to film or TV for a long time, and now a Netflix adaptation (of the beginning of the story) exists.
The adaptation is... OK?
There are a lot of fun things about it. And it really nails a few characters, and reinvents a few other characters in ways that make them more awesome and interesting than they were in the original comics (though overall I'd say there are more importance-weighted misses than hits on characterization).
But I do think there are two extremely core things about the comics that the Netflix adaptation misunderstands, and that add up to a larger weight in the scales than the adaptation's virtues.
I'll probably write a thing about this later, but I'm reluctant to do so now because I don't want to discourage people from watching the show (especially if this causes them to read the comics, and especially especially if it causes them to read the comics before watching the show!), and I don't want to say "your enjoyment was wrong!" to people who love the adaptation.
So as not to be totally mysterious, I'll say that the two deep mistakes the adaptation made are that they misunderstood Morpheus' role in the series (possibly in part because it's a very nonstandard role and isn't highlighted in the first story arc), and that the show has the wrong overall style/genre/focus/heart.
Gaiman is one of four executive producers. He's also one of three script-writers for episode one. My guess is that he saw how hard it would be to do the optimal thing, so decided to do something else just because it's easier; and/or my complaints reflect places where he had to compromise with the other showrunners / stakeholders?