when i'm playing a shoot 'em up...
i want to have dozens of enemy ships heading for me in formation, fragged by my bullets - not only two or five of them most time just moving downwards.
the next thing: i want different weapons. primary and secondary weapons: fine. but i want to upgrade them to fire beams, homing missles, etc. (best by collecting upgrades left by the enemies.)
and finally: i want some extra lives. it's stupid to not feel free to fly some fancy maneuvers because you cannot risk losing health for that you have to beat it on the first attempt and cannot gain life back while in the middle of a mission.