I liked the feel of the plane (felt like climbing / diving not just moving up and down) and the graphics! Reminded me of Time Pilot a bit...
Shooting felt a bit weak with the limited ammo and lack of targeting assistance (might've been cool to have homing missiles in the 1st age and progressively make weapons worse the longer the player survives). Would allow the player to survive a bit deeper into the game - I only ever got to seen the 2nd age.