I truly enjoy Costco. I'm not too sure if the membership fee is worth it mathematically but they carry lots of brands not available at other stores and their own brand, Kirkland is pretty good too.
The customer service is always great and I've never had any problems with returns and exchanges.
They recently opened up a Costco gas station available for their members at a lower price.
My only complain is why they do not accept visa, I for one get charged for transactions on my debit card!