I've done the marathon three times as well. I've enjoyed the race shirts and especially the medals each year. The marathon medal (don't know about the others) has a different aircraft on one side each year and the race logo on the other -- 3-D, very heavy. One of my favorites!
(Oh, and the inaugural event was my very first marathon "way back when" in '98.)
Second the kudos for the Air Force Museum. Great aircraft, WWII exhibits, etc. Can't wait for my husband, the WWII buff, to join me there one year.
Finally, I can't say enough about their support for the back-of-the-packers. They even present a "tail-end Charlie" award to the last marathon finisher -- or have in years past.
I love using this marathon as the opener for my Goofy training: nice long time limit, relaxed race, great medal, and a wonderful way to get the feel for the distance again.
As was stated, there is not much in the way of crowd support because it's on a base, but I enjoy the quiet. And I seem to remember hills, contrary to what everyone has said -- but I'm from a pretty flat area, so perhaps I'm not a good person to judge.
It's definitely not a mega-marathon destination race, like the Elite Rock 'n' Roll series, so if that's what you're looking for, you'd be disappointed, but if you just want a well-run, solidly-supported safe race course, this is a good bet.
Bottom line: My guess is you'll enjoy it!