Using Pack Opener is very simple: hit the button to open a new pack of cards and you'll immediately see the best card of the pack, followed by the rest of the cards. The good part is that all the cards that appear in the game are gold, meaning you'll always get good (or at least well-known) players.
The game even has several interesting achievements. For example, you'll find several achievements that involve acquiring players of different nationalities. You'll also have an achievement for finding a superstar: a player at the level of Cristiano Ronaldo, Messi, or Hazard.
It's hard to call Pack Opener a game ... because there's actually not much game to it. That said, soccer fans will definitely have lots of fun opening up pack after pack of cards of players, and it's all totally free.
Requires Android 4.0.3 or higher