There are a few issues, such as the default enormous size for product pictures, and lack of documentation on theme fixes, but I've tried a lot of different shopping carts over the years, and this one is the easiest to set up and customize.
It's powerful, and flexible. Sure the extensions cost money, but they're pretty cheap, considering what you get, especially since the shopping cart is free. You get more than you pay for.
(Using Woocommerce 2.0x with WordPress 3.5x and it works like a charm.)