Steve,
First off, you definitely have to play all the courses. Some guests don't enjoy Trails as much, but it is really (with a couple of exceptions) a fantastic course and a great compliment to the existing courses. My first impression of Trails was not much. However, the more I played it, the more I appreciate it. It's wide open for the most part off the tees, but in order to have the correct angles into greens (which vary depending upon conditions and hole locations) it effectivelly plays much narrower.
The one thing I would recommend about Trails is to play it in the morning. The final four holes on Trails play into the wind (and a couple uphill) and are that much more difficult after already playing 32 holes. As far as playing 36 goes, make sure you are playing with a hearty group, because 3 days of 36 walking and in the usual windy conditions takes it out of everyone.
Every season (I caddie at Bandon in the summers), I'm with many groups that play TOO MUCH and it affects their performance and experience. It's one thing to play 36 holes back at the home course (with a cart) but an entirely new beast out there. Now, I'm not trying to discourage you from playing 36 each day nor am I saying that you can't, but be realistic depending upon the group that you are going out there with.
As far as OM, I was fortunate to tour the course last September and IMO it is going to be fantastic and all the raves in this thread and others are most deserving. I can't wait to get back out there in a couple weeks and actually have a chance to learn/caddie/play the 10 holes as well as see the new 8.