Dan O'Bannon [Alien, Aliens, Total Recall] wrote an intelligent script that is delivered by a cast of fine actors. Mathilda May is mesmerizing as "space girl." Bless her heart, she spends most of the movie naked as a jaybird. Yet, in spite of this, her nudity never feels gratuitous. She is beautiful, powerful and deadly! I also liked Steve Railsback [Ed Gein, Disturbing Behavior] who plays the captain of the ship. Some reviews I've read are really unkind to him but I think he fills the role nicely and is a good mate for space girl. Patrick Stewart [X-Men, Star Trek: The Next Generation] also has a cameo role that is up to his excellent reputation as an actor. It made me wish he had a bigger role.
Another thing Lifeforce has going for it is the masterful direction of the one and only Tobe Hooper [Texas Chainsaw Massacre, Poltergeist]. He shows remarkable restraint with this film but imbues it with a sense of terror nonetheless. All the scenes where space girl is sucking the life out of someone work very well because of his direction and ability to compose a scene for maximum emotional impact.
I also thought the special effects were very good. The zombies were completely awesome and unique looking. These aren't Romero zombies but something that can only be described as freeze-dried living dead. Love it! The final icing on the cake was an excellent score by legendary composer Henry Mancini. Rarely do horror films get this beautiful of a score. It's a total home run for me.
So, critics be damned. Lifeforce should be on everyone's must-see list. It's unfortunate that this film doesn't get the attention it deserved. I'm trying my best to rectify that situation.
For more info check out the film's entry in IMDB.