The game begins as a very fun and exciting team-based shooter, but changes dramatically and becomes boring.
Suddenly, about 1/8th through the game, the player no longer gets any teammates. It's unbelievable. The game suddenly becomes boring, repetitive and ultimately pointless.
There's not even so much as a battle between the mutants and the evil Illuminati human soldiers. The Illuminati don't come around until the player loses his teammates, so there's never an AI human versus AI human battle in all of the single player.
If the game had kept with it's fast-paced, team-based action, it would have been one of the most exciting single player First Person Shooters ever. However, the game turned around and became a solo hallway-crawler, leaving little to no point in even bothering to finish the game.