This Wall Street Journal article (subscription required) does a quick scan of Wal-Mart's weaknesses:

Wal-Mart is, without question, a fabulously run company. It has, however, but one selling proposition: price. While that's a pretty good one, the company isn't infallible. Same-store sales have been inching down, to the low single-digits. Costco Wholesale, among others, has effectively competed on price, while offering higher-quality goods.

Wal-Mart's store locations aren't always the most convenient. The stores can be dark, hard to navigate and not pristine. The lines are long. The apparel is far from hip.