Admittedly, a Fruit Ninja/Ghostbusters pairing makes more sense than most of the Angry Birds mashups (Angry Birds Transformers? Really?) The idea behind the Fruit Ninja Ghostbusters update is that there are ghost fruit on the loose, and it's up to you to take them out with your Proton Pack blade. There is even a special move, where you can "cross the streams" once per game and unleash a massive attack.
Fruit Ninja is still quite a fun game, so this update is a no-brainer if you're already a fan. Otherwise, there is a free version you can try out on Android, or the full game costs just 99 cents on either Android or iOS. Fruit Ninja also just got a major update to version 2.0, so if you haven't played in a while, there is new stuff to experience.