Well, all Strikers are meant to deal lots of damage, stay out of the front lines, and be very mobile. The three classes do this in different ways that support slightly different styles:

Ranger: Damage bonus to a chosen target, More attacks than other classes (A lot of powers have multiple attacks, secondary attacks, etc.), bonus to AC against opportunity attacks that allows you to move without worrying as much. Good against normal enemies, since they can affect multiple targets in a round

Rogue: Damage bonus from combat advantage (harder to get than Hunter's Quarry/Curse, but more damage), lots of powers that let you move or force movement, lots of shifting powers like Tumble that let you move without taking OAs. Good against tough enemies, since their high damage can be overkill on normal ones, and at moving into and out of the enemy ranks.

Warlock: Damage bonus from Curse (weaker than Quarry/Sneak attack, but you can choose targets and get multiple Curses easily), concealment whenever you move 3 squares, lots of teleportation that doesn't provoke OAs. Good at hit-and run tactics and escaping combat.