My game has a similar design to other space shooters like Galaga and Raiden. Those games, however, are mostly vertical scrolling single-player games, whereas mine is a stationary two player fight. I think my game, while not unique in any way, puts a nice little twist on that genre. The multiplayer components of most space shooter games function exactly the same as the single player portion. The second player just takes control of another ship on the screen. My game's a little different because it is competitive instead of cooperative.
The design itself doesn't really add much to the genre - it's just a simple shooter. I did like the black hole concept I added in to keep people from getting on the same horizontal level and thus being unable to shoot each other. One piece of feedback I got was to make the bullets gravitate towards the black hole in the middle of the screen. I think that would make the game a lot more interesting and strategic since players would be able to curve shots. It adds another level to the game, since right now players can just remain across from each other and block shots indefinitely.
Another piece of feedback I received was to add a cooldown between normal shots. As it is now, the player that shots first and gets the jump will always win. Adding a second between shots will slow it down a bit and create some strategy.