7. Cabal
In the arcade Cabal was a trackball game that was quite unique when compared to more traditional trackball games like Centipede. The ball was used to move the crosshairs around the screen to fire on enemy troops coming in from the distance as the player sat at the bottom of the screen moving from cover to cover. The hard part was the trackball ball also moved the character, meaning that moving and firing was very difficult. The version I played the most however was the NES version where the D-pad replaced the trackball well enough to still really enjoy the game. It might be the first shooter to use a cover mechanic, where barriers were limited by the level the player was on. The cover wasnt invincible either, as the brick wall you got behind took fire it would eventually be broken down to rubble. Like a lot of classic games from the early days I have no idea if Cabal even had an ending, or if the game just got progressively harder until your player just shot himself in frustration. This could be a good reason to update the title.
Update: Due to its early format, any number of themes and stories could be applied to the Cabal formula. The dual joystick game pad along with the triggers could make for a great gaming experience with a definite old school feel. I imagine this as an XBLA Game that passes the initial reminiscent phase (you know that awesome feeling you get playing Streets of Rage II before you realize theres a reason they stopped making these repetitive button mashers in the first place) and players actually play this game for longer than a few hours. The game should keep the same track-shooter feel, but have the player going forward into a 3D environment or valley/corridor.