Brett,
Philip's response captures a lot of it, and there are many factors that make Pine Valley.
It doesn't have a poor hole, and also has regular highlights (whereas Kingston heath doesn't have a poor hole, but doesn't have the highlights, and RM West has the highlights, but also has a few lesser holes).
The set of greens is massively varied, thrilling to play to and on, beautiful to look at.
The heroic moments are many and get your heart racing better than any other course I know.
Getting around the course is an adventure, plenty of coming over rises or around bends to discover what's beyond.
I also think a tremendous amount of what makes the course so brilliant, unmatched IMO, is the combination of extremely wide fairways and severe sandy areas flanking them. That creates an excitement driven by the possibility to be daring, to gain an advantage, knowing the severe punishment of not executing - all the while you could aim down the middle with a safe club all day and needn't go anywhere near the death that awaits. But the holes are just so tempting in what they offer that you are constantly feeling torn between the safe play and the exciting play. The course plays with your heart and your brain constantly. The great courses elicit an emotional reaction, and none does it as well IMO as Pine Valley.
The variety of greens, variety of shot shapes, of landforms, holes shaping left and right, open greens, blocked greens, uphill, downhill, birdie chances, holes that bash you - but all of it with a continuous character...
Being objective, it's extremely well-balanced:
Six "short" holes - 2, 6, 8, 10, 12, 17.
Six "medium" holes - 1, 3, 4, 9, 11, 16.
Six "long" holes - 5, 7, 13, 14, 15, 18.
Six "easy" holes - 6, 8, 10, 11, 12, 17.
Six "moderate" holes - 1, 2, 3, 4, 9, 16.
Six "hard" holes - 5, 7, 13, 14, 15, 18.
Nine open greens - 1, 4, 5, 6, 9, 11, 12, 15, 16.
Nine blocked greens - 2, 3, 7, 10, 13, 14, 17, 18.
There are plenty of quantifiable ways to describe why PV is the best there is, but they can't tell the whole story.