I'm a pretty hard-core Neil Young fan, have faithfully bought his new albums when they have come out since the After the Gold Rush days (30+ years). I personally like the new album quite a lot. Yes, it is a concept album. The critics tend to call it self-indulgent, etc. I personally think they are just being lazy-that is an easy and expected evaluation of a concept album, and doubly easy to label it as such when you haven't really listened to it.
There are no hit singles on this album, nor was there intended to be. Personally I think it is some of the best, and most inventive, songwritiing Young has done in years. If you are looking for recent Neil Young that is more accessible, I would suggest Silver and Gold, his previous album, which pretty much following in the Harvest / Harvest Moon mold.
Incidentally, the CD includes a DVD of a live acoustic concert of Greendale done earilier this year in Dublin. Its supposed to be pretty good, but I haven't had a chance to watch it yet-the weather here is too beautiful now.