I am still so confused on how polarizing "Lifeforce" is. Is it Epic? No. Are there Oscar winning performances? No. But niether is it junk.
Part of the problem with the reception of the movie isn't with the movie but with when it was released. Big things were happening in "Hollywood" in the 80's, Brit films were not one of them. Esp one with a $25M budget.
I found the lore interesting, life stealing aliens who return periodically to Earth to feed and repentish. Human myths and legends skew past visits to "blood sucking vampires" rather than life-essence stealing vampires. For me, this is a nice change-up.
In my experience, people who hate on this movie tend to also be fanbois of The Walking Dead, World War Z, and other plot-holed, random writing quality, fictions that are just as improbable. Personally, I think "Lifeforce" has a lot to offer for a B movie from English cinema.