This is actually the first Petco that I've ever been to (though I've been to a number of Petsmart stores). I have to say that I'm impressed. I don't know if they all look like this, but in comparison to the Petsmart stores, they are a whole lot nicer.
The closest comparison I can think of is that it's a lot like Lowes vs Home Depot, with Petco being more like the cleaner Lowes stores and Petsmart being more like the larger, but dingier Home Depot locations.
It doesn't mean that Petsmart is bad - just that Petco leaves you with a nicer feeling. In fact, it might mean that Petco is more expensive in the end. But it is a heck of a lot better to go inside when the aisles are clean and organized, product is well placed, and things just aren't thrown about and dusty.
Just like Petsmart, they have a loyalty card where you can save a bit of money if you go regularly, and the staff seems nice (they are nice at Petsmart too).