Personally I think the line-up is great. Not a huge fan of the main acts on Saturday but the smaller ones are great even though I've seen most of them at least once already. Crystal Castles, Cut Copy, Warpaint, Tame Impala, Nosaj Thing, Ariel Pink, !!!, Klaxons, The Drums, Glasser and a few other bands I haven't listened to much but would love to check out.
AC always puts on a good show and I missed Arcade Fire at Merriweather, would like to see Mumford & Sons, BSS, PvD, Gogol Bordello (12/30 show was killer), Shpongle, Elbow, Foals, The Radio Dept, and Freelance Whales
Sunday: the Strokes (haven't seen them before), Ratatat, Nas, Bloody Beetroots, Chromeo, Best Coast, Delorean and Menomena.
I mean most of the bands worth seeing have been in DC and I've seen, but half the fun of a festival is checking out new bands, seeing those you've missed when they came through or seeing your favorite bands again. I think it would be worth going if I wasn't planning on going to Sasquatch a month later.