There are several ways this project could be improved; why don't you try one or more of them?
Add an achievements system like Game Center or Open Feint
Add a way to match up against other players
If you want a real challenge, create a multiplayer mode where both players receive the same level and can see each other's ship on the screen
Add a local high score chart as well so that the player can see their own score history
Use some analytics to rate the player based on the global scores, for example, "You rank 152 out of 893 players"