I was reading this article "Does originality matter?" on "Roach Puppy Games". Chris compared the popular "Angry Bird" game with an earlier game called "Crush the Castle" and it's quite obvious which one should be the first to come up with the original idea. However we all know the huge difference between the result.
That inspired me a lot. As long as yours is better, who cares if you are the first one who comes up with the idea?
Then, how to make your application better?
I can think of one thing - the most important factor that makes Apple so different from any other companies - the user experience. You could have spent 90% of your time in your game design, but it's the front end 10% user experience that matters. Even if your game have much more complexity/feature/images than others, if it can't provide a smooth experience, it definitely won't stand out from the crowd!