Holbrob and Chiney, et al.,
I'm a Gold Medallion on Delta (from last year; will make Platinum in July, most likely), and am on them almost every week from work.
Delta has some issues, as does almost any US airline these days, but for the most part the experience is painless. Chiney's right that the flight will be a 767-300ER or 767-400 (what I was on a couple months back). The -400 is a fine aircraft, but most of the -300s are older, and in need of some upgrade (at least once a month I have a seat that automatically reclines for me).
Thanks to my medallion status, I'm able to fly first or business class most of the time, but do still fly coach occasionally. I can say without a doubt that the food for sale in coach is BETTER than the fare served in first class (though why that is I have no idea; I'd prefer the food for pay).
As for seating, if it is indeed a -300 and you're lucky, I'd suggest seats 27A or 27G. These are exit seats, and have no seat in front of them giving you a little room to stretch. I can tell you comfort wise that Delta is at least 50% better than US Airways, and 100% better than Northwest (which I just flew yesterday), IMHO.
Best of luck to you!
RD
(edited to add missing words...)