Let's look at the base gameplay mechanics: The objects used in the game are:
Player Controlled Paddle
A.I. Controlled Paddle
Pong works by letting the player control a paddle that can either move left or right across the screen. There's another Paddle that is A.I. controlled that the player is trying to beat. The player can beat the other paddle by hitting a ball that bounces across the screen past it. The player loses if the ball goes past his paddle.
In all games, Polish is extremely important. However in Simple Games like pong it's even more important. The simpler your game, the more polish you have to put in to the Main Menu, Score System, Game Over Screen, Options, etc. so the player doesn't feel like your game is "Cheap". The larger your game gets, the less important this *seems to become. I've seen a lot of large games with fun gameplay mechanics feel stale and boring because it's a pain to navigate, there's key features missing from important parts of the game that don't concern the interesting "hook", etc. It should be even more important than in simple games for you to polish your bigger games as much as possible. No one will play your amazing game if your main menu doesn't move at all, and the "base" features don't work. By base features, I mean you found an interesting hook on a genre. You spent almost all your time improving that hook, however the base features of the genre are poorly implemented. You see this all the time, even with triple A games.
In Pong, you'd probably want a Simple UI. An easy trick about UI's is to look at the "feel" of your game. Pong feels simple yet interesting. So I'd make a GUI with a Simple layout, with White and Blue (Or Black and Neon) colors. There'd be subtle animations when your cursor hovered over a button. I took the "feel" of pong, a simple and easy to play game, and try'd to put it into my UI. This can be applied to all UI's. One thing that can make your UI better also it to have an small Mini Game or Easter Egg. Perhaps when the player puts their cursor over a certain part of the screen a small reference to your favorite video game appears. Do something to connect with the player.
The Implementation of pong has to be very good also. Considering how simple pong is in gameplay mechanics, many people underestimate their implementation. You should tweak your controls, AI, Art, and Sound hugely in pong, because they're the make or break factors of the game. There's also very little of every thing mentioned above, so you should have enough tweaking time to get it just about perfect. Imagine playing Battlefield with terrible AI. It'd take away from the fun of the game a large amount because of how important it is. Now imagine playing pong with terrible AI, however in Pong the AI is too hard. Now your player can never beat it. He'll eventually get mad and just stop playing altogether. That's why tweaking is important. The same can be said for audio: if your sound is obnoxious, the player won't play because of how annoying he thinks your music is.
[size=7]Fin (For Now.....)
So, I hope you enjoyed pong. I'll be updating a lot, however I need some time to think about smaller details. Feel free to PM me with questions about Mechanics and Art!