Romac, you do not live in germany?
Years ago, a little firm from Bochum, Germany, called "phenomedia" started a new genre.
They published a game "moorhuhn".
It was not 3D. Just simple sprites, layers and mouse detection.
Monster Invasion followed this rule. The landscapes and most of the optical fx are sprites.
Just the monsters and ufo are polygons. The player will not have the possibility to move forward.
You can only scroll left and right.