100 Invaders is an excellent Space Invaders-style game with some added twists to keep the gameplay fresh.
The basics are all here formations of invaders approaching from the top, and your lonely ship trying to destroy them all. In 100 Invaders, once your first wave of invaders are destroyed, they start to return as ghosts! These are larger, and nee accurate shots to their centers to be killed.
When killed, the ghosts release pods, which if shot a few times turn into power-ups. These let you move up and down, as well as left and right. The more power-ups you collect, the more freedom you have.
The game has a cool flickery appearance, and while it can get hectic, you can always see what's coming for you. There are enough different enemies to keep things interesting, and levels do end, giving you a much need rest during the action.
There are so many Space Invaders clones, that 100 Invaders with its fresh take on the idea is well worth downloading.