From the app listing:
This is where your Game starts. The new, improved Game Reward scheme is a great way to get even more out of shopping with Game. Collect points on everything you buy in-store and online. It’s simple to join, just download this App and fill in your details, then use the App whenever you shop.
The other interesting wrinkle here is that the application is only for Windows Phone 8. While many Windows Phone watchers were expecting Windows Phone 8 only gaming titles, to have an informative application such as Game Reward limited to the new handsets is an interesting choice.
I presume this is down to the ease of developing a cross platform client - the apps is also available in the Apple App Store and through Google Play. If the balance between having 'apps at launch' is the sacrifice of an initial launch on Windows Phone 7, we're going to see a lot more WP8 only apps over the next weeks and months.
You can download the app direct from the Windows Store.