It's not clear to me why Lost in Space has been slammed so much by critics. The effects are great, the plot has its moments, and the acting is mediocre. That doesn't seem much different from many blockbusters that have received far more positive reviews, such as Independence Day or Mission: Impossible.
The plot: Humans have exhausted the resources of Earth and need to colonise other planets in order to continue their polluting existence. The area of space humans are interested in colonising is known as Alpha Prime, which requires a ten year journey by "normal" space flight. An "hypergate" is being constructed that will enable the inhabitants of Earth to travel to Alpha Prime in no time, but for it to work, the gate has to exist at both ends. The Robinson Family, John (William Hurt), Maureen (Mimi Rogers), Judy (Heather Graham), Penny (Lacey Chabert), and Will (Jack Johnson), are the ones responsible for building the hypergate at the Alpha Prime end (and this is the most incredulous part of the movie).
With Major Don West (Matt LeBlanc) piloting Jupiter II, the spacecraft carrying the Robinsons begins its ten year journey to Alpha Prime. However, the Global Alliance undertaking this colonisation mission has an enemy, the Global Sedition, who recruit Dr. Smith (Gary Oldman) to sabotage the mission and kill the Robinsons. When Smith himself is double crossed and left on the spaceship, he helps avert the Robinson family destruction. In doing so, the Robinson family find themselves pulled towards a sun and have to engage the hyperdrive to escape. But as John Robinson says at the beginning of the movie, using the hyperdrive without a hypergate at other end will result in uncertainty in the final destination, and the Robinsons end up being lost in space.
At this point, the story begins to lose cohesion. As the family wander around space, they encounter a ship from their future invested with heat-seeking silicon-based spider-like creatures and a fuzzy animated monkey-like creature who comes to be known as "Blawp". The ship from the future is no coincidence: the Robinsons find that they're caught in a time bubble whose originator is intent on going back in time to prevent the Robinsons from beginning their mission. But unknown to everyone, there's a fly, or should I say spider, in every dab of science-fiction ointment.
While the futuristic set design is what makes this movie worth watching, the acting by most of the characters is terrible. Oldman, Chabert, and Johnson are the ones that shine, while the rest of the cast come off as uninspired. The plot has its moments, but the ending is too weak. Worth the matinee fare on the big screen.