What's the skinny on BJ's? Is it a Costco knockoff or what?

Never been to one. I was a Costco member in Portland, OR. There's just the two of us so I had no use for megapacks of whatever, but for some clothes, the occasional electronics or home goods purchase, the three (now five) buck rotisserie chicken, prime grade beef and other meats, and of course that $1 hot dog, I was there. What's the deal with BJ's? Are their prices good? Anything they're particularly good for? Do they have stattions throughout offering samples?

Note: Please don't compareto Spam's club or whatever the fuck that place is as I have never set foot in one.)