Same deal as previous offers for Titanfall and Battlefield 4; download the game, and once you boot it up the clock starts running down in real-time. A bit like 24, but probably less tense.
Plants vs. Zombies: Garden Warfare is the third-person shooter spin-off of the popular lane strategy game. Somewhat surprisingly it was pretty well received upon release. Might be worth checking out if you fancy a fun, very silly bout of action.
Remember, grab it before August 15 if you want to check the game out.