Hmm. How about some real information rather than opinions?
The film opens with the Enterprise E on a testing mission. They get a message reporting a second Borg incursion, but are told to remain at their position on their current mission. Captain Picard thinks Starfleet doesn't trust him, a one-time borg drone, to captain his ship effectively. Picard goes against orders and orders the ship to travel at high warp to earth.
As the Enterprise enters the solar system, we see the borg cube, surrounded by Federation ships. The Defiant is badly damaged, and Worf, the commanding officer of the Defiant, is beamed aboard. Picard takes control of the fleet and orders them to target a specific area of the cube. The fleet responds, and the cube is destroyed. As it explodes, a sphere exits the cube and flies towards earth. As the Enterprise follows, they are caught in the wake of the sphere as it travels back in time.
As they enter real space after the travelling to the mid-21st century, they find the sphere attacking a point on the surface. They destroy the sphere, and beam an away team down to figure out what the Borg were attacking.
The away team finds that the first warp ship has been damaged, days before it was to make its maiden voyage. The voyage is important because it was to signal to the Vulcans, who happened to be in the system at the time, that Humans were an advanced civilization. If this were to not happen, Humans would remain at war and history would be altered.
Back on the Enterprise, it becomes apparent that before the sphere was destroyed a few borg beamed over and have begun assimilating the crew.
The crew must both help repair the warp ship in order to preserve the timeline, and battle the Borg who have begun to take over their ship.