Hi there. Sorry your having trouble with the app. I can't tell from your message whether your getting stuck during the upgrade/install download process (where the icon gets a blue bar across the bottom to indicate the progress) or if the problem is when you click on the icon to run the app.
The app is fairly large at 520mb and will take between 15 minutes and an hour depending upon your connection speed. If the connection is interrupted it can cause the download to stop. Sometime rebooting the phone will help. Sometimes you have to delete and attempt to reinstall the app. If that doesn't help, you can use iTunes to download the app and then sync it to you phone.
If the problem is with the app hanging after you click on the icon, then the download/installation may have become corrupted. Removing the app and then reinstalling it should do the trick.
Hope this help.