Before X-COM the same author had much simpler games called "Rebel Star" and "Laser Squad" (only the 2D tactics, and several fixed missions, no management), which I liked more than X-COM.
I liked their funny targetting interface, which was different than in roguelikes (in the targetting mode, each creature was shown as a circle, small creatures were small circles and large creatures were large circles, you could shoot at any pixel, some deviation was added to the direction, and the game checked which circle or wall/furniture was actually touched first by the straight line).