I don't have a problem with Wal-Mart itself.
I hate the experience of going to the(big) Wal-Mart closest to me, so going there is a last resort.
On the other hand, the Wal-Mart right by my work has the same prices, 90% of the selection, and is always way less busy. They also have the least expensive gas in town(and put enough pricing pressure on the other stations in town that the middle-of-nowhere town where I work tends to have the best gas prices in the area) although you take your life in your hands trying to get in and out of the gas station at a busy time.
I admit to never having checked SKUs, but even if Wal-Mart has unique SKUs I kind of find it hard to believe that there's a huge difference in major brands sold there vs. other sources. The big brands do have a repuation to uphold, after all.
Someone mentioned cameras above. I've owned, well, a fair few cameras in my life. Somewhere or another I have a Nikon N65 with a receipt from a local camera store in the box from around 2004. I have another N65 kit with a Wal-Mart receipt in the box. I have never looked at the SKUs, but an N65 is an N65. It's a consumer grade SLR with all the good and bad that comes with it. They have the same crummy variable aperture kit lens. The camera store one was $275, and the Wal-Mart one $200. The receipt shows that the camera store also threw in a UV filter, a cap keeper, a battery, and two rolls of film(plus developing coupons are still in the box) for no extra. Considering all of that, and the fact that the camera store could have actually helped the person use the camera properly, I'd say the camera store buyer got the better deal despite the extra up-front cost.
We shop at Sam's club a lot too, and are generally happy with a lot of the "Members Mark" branded products. My go to coffee is their store brand Columbian Supreme. I'm not a coffee snob by any means, but after changing a few years ago to drinking black I've come to like darker/bolder roasts. I have a few coworkers who are coffee snobs, and I've given then cups of this without telling them what it was-they were favorably impressed.