Q:

2002/2003 PC Game about Super-soldiers winning against aliens but losing Earth coming back?

A long time ago I remember playing a PC game around the time of HALO: COMBAT EVOLVED clones... one stood out in particular.
The story preface revolves around a war between Earth and aliens. Humans win by the skin of their teeth, but when the remains of the fleet comes back, they find that the war was a diversion and the aliens took Earth while they were away.
The commander during his speech calls his supersoldiers "his children" and the entire game is a mix between shooter, vehicular combat, squad tactics, and a light flight combat simulator to kill aliens by the hundreds.
It was interesting at the time because I remember the game letting me peek by leaning out of corners, having very tactical gameplay, and squad multiplayer with 8v8 and later I think 16v16 matches with Gamespy.
Notes: 1st/3rd person shooter, PC, game came out around 2002/2003 

A:

The game you are looking for just might be Breed, released in 2004.

Plot synopsis
After their year-long journey the fleet arrived at Besalius in 2604
and swiftly engaged the Breed presence across the system. The battle
was long and hard, as the Breed did not give up the system without a
fight; their lack of intelligence was more than compensated by their
ferocious nature in battle. This conflict with the Breed would come to
be known as the Colony War.
The humans resources were drastically drained during this rigorous
fight and the USC forces are stretched to breaking point. In 2624 the
USC forces claimed victory in Besalius, but it was not without cost –
the colonies had been devastated and the fleet badly damaged to a
point that only the USC Darwin was capable of making the journey back
to Earth. Captained by Saul Richter (A legend now with over two
hundred victories against the Breed under his belt) war weary and
battle scarred, the ship and remaining crew began their return
journey.
In 2625 that the victorious veterans of Besalius finally returned home
expecting a heroes' welcome. Instead, the crew of the Darwin found
their world on fire, that in their 20-year absence, the Breed had
conquered Earth. The Colony War on Besalius was nothing more than a
diversionary tactic – a plan to pull the bulk of Earth's defense
forces away, leaving it ripe for invasion. The human population had
been enslaved or devastated, the survivors had been enslaved by the
Breed in forced labor camps.

