My personal thoughts are that a hard course is one that keeps you on your toes with subtle and not so subtle changes of direction and wind that can catch you out.
Ones that just are a constant raft of over 40yds targets are boring and can just switch off. Having the occasional gimmie keeps the interest for lower grades, I mean say out of 4 of each positionals 1 should be possible for all to hit.
I enjoy putting courses out, this year's Winter course I think was one of our best. Not cleared but wind and angle changes caught even the top grades out.