There's nothing wrong necessarily with the game, but I do have a few gripes:
1. This type of game has been done COUNTLESS times. In order to make your game stand out, you need to really do something with it that can be considered unique or different from the norm if you want people to really like it and choose it over another game of the same type.
2. There's no menu screen or any type of instructions. You start playing the game immediately when it's done loading.
3. There's no sound of any sort.
4. There's no reward or reason to keep on playing other than a high score that also isn't beneficial to the player. You just shoot stuff until either you die, or the timer runs out.