My impression based on seeing Doonbeg prior to construction and during three subsequent visits is that the project team struggled from the very beginning.
First, Norman went overboard with his hype about the land at Doonbeg prior to construction. Knowledgeable observers in Ireland knew it was a good but not great piece of land.
In a sense, the marketing hype cheapened the course, at least for me. Sean Walsh was justified nominating Inch as the best site in the world to build a golf course; Norman had no business making the same claim for Doonbeg. It's not in the same universe as Inch or even Castlegregory, I suspect.
This was especially true given the environmental restrictions everyone knew would be enforced from the very beginning. In short, you had to move some dirt - actually sand - to get 18 holes, and the permitting restrictions wouldn't going to allow all you might like done.
Then, too, I think the project team had the wrong vision. With the skills of Norman in mind, they set out to challenge the very best players. But, they neglected the real people who would play the course - the mid handicappers.
Along the way the project team did correct some of their early mistakes, though with all the changes I'm still not sure they got the green complex and bunker scheme on #9 right.
For comparison's sake, one only needs to look up the road. Lahinch can challenge the low handicapper but it has the charm to entice the mid handicapper to return again and again. Doonbeg today can't make the same claim.