I've only shopped at Wal-Mart Super Center (#2 on the worst list) and Food Lion (#8), so would have to say the ratings are well deserved. Counting Walmart, I've shopped at four of them, and would agree with you. For those of you who've never had the pleasure, imagine having to buy your groceries from the DMV.
The FoodLion by me is decent. Not an upscale shopping experience by any means, but decent. It's clean, well-stocked, the selection is adequate, and the prices are pretty good.
BUT, I don't live in a "food desert" or in an (shall I say) "urban environment". Likely has more to do with it, than anything else.