I rate them as very good. They are unfailingly polite, their prices are competitive, and I've never taken delivery from them of an unsatisfactory product.
I have two minor complaints: first, their website is clunky. Navigating it takes time, pages don't always download, and occasionally, I've started placing an order only to have everything lost. That's a minor annoyance.
The other minor annoyance comes with back ordered ammunition. One can sometimes wait many months for a back order to be filled. Checking their site will give you estimated delivery dates that turn out to be wildly optimistic, having no relationship with reality. An example, I ordered some Magtech cleanrange .38 special ammunition from them in May, it still hasn't been delivered. Most recently, they estimated a November 19 shipment date. That's come and gone and, the ammo is still backordered with no foreseeable delivery. I've had the experience several times where something I've ordered from Midway has gone into infinite back order status and, after sitting around waiting for it for a few months, I've been able to purchase the same item as an "in stock" item from another distributor like Cabelas.