With the caveat that not every store is the same, not every experience you or I will have on any given day will be the same, not every product is perfect, and with the understanding that everyone is entitled to their opinion...
No one has mentioned the experience of being a Costco employee. It's not perfect for everyone, like any employer, but I've got two brothers currently working at Costco, one as a stocker and one as a manager, and a third brother who rose to Asst. Store Mgr. before leaving for greener pastures. They pay good wages, have good benefits, and for the most part treat employees well. You can make a good career at Costco if you've got what it takes.
Also, no one mentioned the pharmacy. You don't have to be a member to use the pharmacy. Costco's no-insurance drug prices are often lower than your medical plan or other pharmacies. But you've got to shop the price of individual drugs using a site like GoodRX, Costco doesn't always have the lowest price.
As for the return policy, they reigned that in on electronics a number of years ago but still have liberal returns on most everything else. We've all heard the shocking stories, and my brothers confirm the truth to many of them. I once bought stinky pork ribs, they give me a refund no problem and I didn't have to bring the meat back to the store.
As for checking receipts at the door, despite what they say about "accuracy" and the fact that they do occasionally find errors that redound to the customer's benefit (e.g. forgot to pick up your $100 restaurant gift cards after check-out), we all know it's got a lot to do with loss prevention, and they can require it as a member-only store. I agree that it makes me feel like they don't trust me, but the fact is they don't! Again, lots of horror stories from my brothers about the things people try to get away with at the register and at the exit.
As for wine, Costco has some renowned wine buyers who scour the globe looking for very good wines and then sell them for very good prices.
As for store arrangement, someone earlier said it's haphazard. It may feel that way to a shopper, but it's strategically laid out and frequently rearranged to maximize your exploration of the store, keeping you there longer in the hopes that you buy more.
As for gas, when prices go up, Costco gas is almost always cheaper and it's good quality Top Tier gas. They're not trying to turn a big profit on gas, it's an enticement to get you to the store. In fact, it's often said that most profits come from selling memberships, not products.