Finally came back to this after dropping it once the first season was done. Marathoned the other three seasons and it's OK.
Was glad to see that they included some of the iconic scenes from the source material, albeit usually in different contexts.
Was not happy with what they did with the Cassidy character by turning him into such a good guy, that pretty much entirely misses the point of who he is. Removing his strength seemed unnecessary. Killing him off in the way they did was just straight up pandering.
No complaints about any of the actors, they all did a fine job. The Saint was especially wonderfully acted, as was Herr Starr. Jodie was probably the weakest performance, as well as a mis-cast.
Overall, they did a OK job converting the story to a series format. They certainly didn't ruin it as feared.