There are loads of Geometry Wars clones out there. Some of them are straight rip-offs. Some of them try to add their own little twist on the formula... and fail. But sometimes they get it right.
The curiously named vel.shock() is one such Geometry Wars clone that gets it right. The mouse controls your little ship as it whizzes around the arena. Stationary enemy turrets spawn in and start shooting at you.
Thing is, you can't shoot back. You have to use your shield to deflect the turret fire back at the enemies. Clear the screen and you move on to the next wave.
There's a slight delay as your shield recharges in between uses, so you can't just mash it and hope to survive. This creates a nice balance between wanting to stay out of trouble and needing to get in the line of fire so you can actually destroy the enemy.
Check it out.