Now that I'm starting to step into web development, I'm always getting introduced to new things, especially with things that as a Web Designer I've been using for years but never actually knew how powerful these things were.
The UI is very responsive and smooth, it works with PayPal, Google and Amazon payment gateways.
It's very well documented and has new features being added, if you want to build a simple shopping cart solution for a client then this is something new to try out.
Apart from that this works great.
Check out simpleCart.