You start off the game on a bus and you are introduced to our 4 characters.
Roland, the soldier. Special ability is Scorpio Turret. Roland can deploy a turret to kill enemies, and with skill points, regenerate health, regenerate ammo, shoot missiles and even revive fallen team mates in the vicinity.
Mordecai, the hunter. Special ability is Bloodwing. Mordecai can summon a bird that attacks enemies for you.
Lilith, the siren. Special ability is Phasewalk. Lilith can enter an alternate dimesion in which she can move faster and damage enemies when she exits.
Brick, the berserker. Special ability is Berserk. Brick temporarily enters a state in which he only uses his fists, but with great damage and he also has rapid health regeneration in "berserk" mode.
> If it is you first time to the game, and you are looking for an easier character, I recommend Roland, as getting out of a sticky situation can simply being deploying your turret. If you upgrade the turret (including the cool down options) you will have "another soldier on the field".