I ran OBX 3 years ago, it was my first (and to date, only) marathon. It was awesome! My brother has run several (5 or so) marathons and OBX is his favorite. The first 13 miles are great, you run along the Sound, through neighborhoods with people out cheering you on. The back half is mainly a road race, but it is still good. The bridge into Manteo is a killer. The day we ran was perfect, 55 degrees or so, however, I had a friend run it last year, or the year before, and she stated that it was too hot, above 70 degrees I think. I agree with JDF in that I have been told the wind can be a huge problem at OBX.
All and all,I would recommend it and I may do it again this year. It's a great run and the family loves being at the beach.