Impact is based on an Atari game of the same name, which is based on Arkanoid, which is based on Breakout!
The gameplay is very similar to Arkanoid; you must destroy the bricks in standard Breakout fashion, kill the aliens (or avoid them) and collect the falling tokens.
There are four types of brick: standard, multi-hit, indestructable and invisible. The latter can be made visible by use of an icon. The aliens wobble down the screen getting in the way and deflecting your ball.
Instead of collecting a laser gun, you must collect enough of the U-shaped tokens to 'buy' the laser. There are nine icons you can attain in total, randing from 'slow down', through 'wide bat' to 'power ball'. When a screen is completed, you are told its access code, this then enables you to start again at that screen.
The sprites move speedily and are fairly smooth, if rather on the small size, and I thought that some of the ball bounces were rather jerky.
Impact's best feature is its size - with 80 screens, a screen editor, an intelligent demo mode and numerous cheat options.
Impact is a good game. I prefer the 'feel' of Arkanoid but like the extra features provided by Impact. In the end you pays your money and takes your choice, Me? I like 'em both!