I agree with the sentiment in favor of hole 13. The best par 5s create a challenge on each of the three shots, and 13 surely passes this test. The drive is strategic (and very attractive to boot) and leaves a lot of room out to the right. If you do bail right though the slope of the fairway and angle slightly exaggerate the difficulty of the lay up, which requires a decision (primarily regarding the length of the lay up). Finally, the approach is either from a very difficult lie or is nearly/entirely blind.
One criticism could be that of the above choices for the lay up, none are rewarded with relatively easy approaches. If I remember correctly, essentially all of the approaches from about 160 and in have multiple degrees of difficulty. I guess if your drive is long enough you could attempt a bolder lay up to the small, somewhat flat portion of the fairway just in front of and below the green. That said I just love the challenge of decision and execution present in each shot.
A hole that few have mentioned, and I think it is because it is almost unanimously regarded as the best hole on the course, is hole 6. Another perfectly placed carry bunker with the kick slope on the back side serves as the perfect directional guide. The approach is one of the most attractive and difficult I have seen. I only wish we had seen a back left hole location where you could use the steep slope to feed it down while risking a slight pull into the left hand bunker.
As Patrick stated before, there is not a single hole on the course that qualifies as weak. The only one we could come up with is hole 1, but with the massively built up slope on the left hand side of the green and the awkward drive, there is no way it could be called ordinary. It was discussed in the course tours by Ran and Dan that holes 12 and 17 were built on the least interesting locales on the site, but each have tremendously constructed green complexes that make them interesting holes.
I don't think I have enough points of reference in order to come up with a Doak number, but as George said, it seems the definition of an 8 describes Lawsonia accurately. Regardless of any rating, the course is fun, unique, challenging, and beautiful. If a course accomplishes all of those things, it belongs in a pretty lofty peer group.