Space Ace is a first-person space combat game by prolific British game developer Mike Singleton. The player floats through a game space filled with enemy craft, able to fly in eight directions using the keyboard's number pad, but unable to thrust towards or away from the enemy craft.
Likewise, the enemy drift past parallel to the player, unchanging in speed or vector. The challenge here is to line up your targeting reticle with the circles at the center of an enemy craft and fire. As an aid you can, with the space bar, set a given directional key as your set vector - a cruise control, if you will, providing constant movement in that direction until you choose to cancel it.
Once you've destroyed one ship, the rest will begin to fire at a constant rate. Every second or so they'll send off a ring of shots spreading from the center of the ship that - if they intersect with your reticule - count as a hit on your shields. The challenge is to take out as many ships as possible before your shields are destroyed.
I should point out here that the enemy ships have no AI that responds to player actions. They will drift in their assigned direction endlessly, scrolling from one edge of the playfield to the other, mindlessly firing their weapons on a set schedule.
If you do get hit, there is no grace period. As soon as the collision animation - a flashing screen - completes, you can immediately get hit by another of the ring's shots if they're close enough together. Considering you need to shoot the ships in their center - where the ring originates - to have any effect, it's not unknown for a single shot to burn through the entirety of your shield before you can meaningfully react.
Visually it's not bad for a Commodore PET game - the enemy ships are large, and while they all basically look like TIE Fighters, varied in visual design. The sound isn't bad for the era either. It's just the gameplay - basically unresponsive to the player - that's supremely unimpressive.