This game has nothing to do with the arcade classic Defender. More's the pity, It's a simple shoot-the-aliens affair, the only point of interest being the 3D view of the action.
At first sight it looks quite good. The planet you're flying over scrolls beneath you in the form of a moving grid, and the enemy craft loom larger and larger as they get closer.
But in actual playability, the game falls down. As is usual with 3D games, you aim by moving a crosshair sight to the spot you want to hit.
But in this version the sight jerks along sluggishly and there's an annoying delay between pressing the fire button and the actual shot. And your motion is interrupted every time the approaching craft opens fire, which is poor programming.