I've never been that big on video/computer games but I used to have a PS2 and my absolute fav game was Star Wars Battlefront II, released by Pandemic in 2005.
You could choose to play as three different classes of soldier and fight for the rebels, the Imperials, the Republic or the battle droids.
As you played and gained points by killing the enemy, you could unlock a fourth and fifth class of soldier. You could also play as a hero or villain - such as Darth Vader, Luke Skywalker, Princess Leia, etc.
There was something absolutely awesome playing as Darth Vader and cutting down or force-choking rebel soldiers on the Tantive IV.
There were space battles, a chance to hunt indigenous life-forms, or you could play a kinda galaxy conquest. You could also join up online with other players.
The first Battlefront was pretty good, too, although it lacked a lot of the sequel's features.