I'm still worried about the sheer number of puzzles. I don't think the comparison to Myst will hold true at all. Myst has only a handful of sprawling and memorable puzzles. The sheer number of puzzles in The Witness seems to imply that they will feel largely forgettable.
I hope I'm wrong, but that's the impression I'm getting.
From what we know, many of the puzzles are bite-sized, but not self-contained. The puzzles build on each other. So you may not remember a specific puzzle that you solved, but you will definitely remember the concepts that the puzzle imparted on you (since understanding those concepts is key to solving subsequent puzzles).
And I'm sure there are many significant, sprawling puzzles to solve as well.