Tennis: ...that's what it is
For the rest it mostly resembles a beefed up version of pong. The differences are the perspective, the rules that apply to the game of tennis and the visual attractiveness of the game. The graphics consist of a green screen (the field), white lines (the edges of the field and the net), and pink and blue characters.
This is why I give it a six. It doesn't offer a lot of depth nor addictiveness. The game could be nice if you're not competing against the AI but a real person, but that's where it ends.