Cactus is one of the most interesting indie developers around at the moment, and PING PONG! is one of the best offerings yet.
PING PONG! is obviously very retro, featuring graphics and music that wouldn't have looked out of place in 1983, but it's a surprisingly playable little game. Control is via the keyboard, you hit the ball with one key, and there are four effects you can add - smash, chop, loop and slow. These alter the rhythm of the game, and make returns harder. If you hit the ball seven times in a row, you'll do a 'super smash', but it's hard to do!
PING PONG! has three game modes: Single player, two player and training. Training will acquaint you well with the tactics or the game so is worth playing through. In two player more you'll be sharing a keyboard, and for some reason there are no instructions about the keys!
One player mode is hard, too. It will take some effort to win matches.
PING PONG! won't be to everyone's tastes, the lack of instructions is annoying and it's difficult. However, if you like old school games, you'll really enjoy it!