Fun Fact: Life Force on the NES was based on a third iteration of the Salamander game, which took advantage of differences between the Japanese and American arcade releases by combining the best of both worlds.
Life Force felt like a sequel to the Gradius series of space shooters when it was released in the North American market, but was actually based on a Japanese arcade game called Salamander which was considered more of a spin-off to the Gradius arcade games.
Life Force alternated between side- and vertical-scrolling levels, and unlike the Gradius games the player picked up from where they died rather than being returned to an earlier point in the level. That act of kindness might have been motivated by how insane some of the levels were, many of which featured organic environments that “grew” surfaces for the player to crash into.
The 2-player mode made for fun competition to grab the power-up capsules that added new weapons to the players' ships.