I think Costco is a pretty cool store. I think it makes sense to buy certain items in bulk and I can usually see the savings, but there are definitely times when I'd be fine with buying just a can of olives as opposed to a 55 gallon drum of them.
Why do so many people like Costco? The answer is easy, free samples! If you play your cards right, you can eat an entire meal by the time you leave the store. If you wear a reversible jacket then you are guaranteed to leave with a full stomach.
A few things I don't care for are how you have to show your membership card when you come in the store. I guess that makes some members feel more important like they are part of an exclusive club. I'm also not a fan of the security receipt check when you leave the building. I think the transaction should be over once you pay the cashier. Despite these minor pet peeves, I still think Costco is a cool store even though it is not the main grocery store we usually shop at.
The danger with Costco is that you may plan on going in for milk and chips, but you end up leaving with a 48" flat screen TV, pool table, and pre-lit Christmas tree because they were on sale. You never know what you might find when you go. There are few other stores where you can buy orange juice, play ground equipment, diamond rings, and a bouquet of flowers all at the same place.