S2 runs Samsung's own Tizen operating system. It currently has a lot less apps than Android Wear or Apple's Watch OS and a lot of third-party apps perform badly on the device. It's unclear if developers will start to develop Tizen apps in the near future.
There are two buttons on the side for navigation - a digital crown that you can rotate and press in and a simple, tactile button. While the button is pretty straightforward using the digital crown is not an intuitive way to navigate.