I think the reviws are harsh, its not brilliant, its just fun, and not that bad seing as it was made in 2003.
After realizing the Planet Express delivery company has been losing money for blatantly obvious reasons (such as using a giant spaceship to hand-deliver single packages and the crew never actually collecting money for deliveries), Professor Hubert Farnsworth sells the company to Mom. With her purchase of Planet Express, Mom now owns over 50% of the planet Earth, and becomes its supreme ruler, taking all humans for slaves and instituting a curfew with 'hoverbot death troopers' patrolling the streets. Fry, Leela, Bender and Farnsworth attempt to escape Earth but the ship is inexplicably (for now) broken and scorched so whilst the others repair the ship, Fry is sent to find a hammer. However, he is killed when the two-ton pile of steel and junk (the professor set this up to test an invention) the hammer was supporting falls on him. He is brought back to life by the Professor's "Re-Animator" and finds all the Professor's tools to fix the ship. Alas, the Professor couldn't fix the dark matter engine so Fry must go to the pawn shop and reclaim the back-up engine. Once he does so they escape Earth with the Re-Animator and the gun the professor pawned the back-up engine for.
Mom's plan is bigger than the mere conquest of Earth; she plans to turn the planet Earth into a gigantic Warship to conquer the universe. However, in order to move the entire planet off its orbit, she requires a large Dark Matter engine, that only Professor Hubert Farnsworth knows how to build. She captures the Planet Express Ship in a tractor beam from a scrapyard on a desert asteroid. Bender escapes with the Re-Animator and shuts down the tractor beam. Mom's ship (in the shape of Mom's head) captures the Planet Express Ship in its mouth and Mom and her sons board the Planet Express ship. They cut off the Professor's head and put it in a jar before hurling the Planet Express Ship into the sun.
In a bizarre twist, the sun actually has a habitable surface, where the Sun People live in fear of the Mighty Sun God that has killed much of the star's population and created an undead army out of their bones. Leela defeats him, in exchange for Dark Matter to fuel up the ship, and the crew heads to the planet Bogad (Dagobah spelled backwards minus two letters), home of Professor Farnsworth's mentor Adoy (Yoda spelled backwards), presumed to be the only person capable of hatching a plan to solve the situation. As the crew journeys to Bogad, Mom succeeds in powering up the Earth's Dark Matter engine and proceeds to destroy nearby planets.
On Bogad, the crew meets Adoy, who reveals he's invented a time machine capable of sending them back in time and stop Mom before she became unstoppable. The ship and crew travel into the past but arrive completely out of control, crashing the broken, scorched ship inside the Planet Express hangar with not much time left to prevent the original sale of Planet Express. They then leave in their original ship, thus explaining how the broken ship got broken in the first place.
The crew arrives at Mom's Company just in time to prevent the sale, however Mom forces them to fight the robot Destructor from "Raging Bender". The crew manages to defeat him, but then they are crushed and killed by Mom's sons. Professor Hubert Farnsworth has a face-off with Mom and then returns to Planet Express to give his employees some good news. The cutscene shown at the end is actually the first cutscene from the beginning. The game ends the way it began, returning to Level 1 and completing the circle in the timeline (creating an infinite loop).