What is the difference between gears of war 2 limited edition and normal edition

the limited edition comes with extras.

At the game's release, Epic Games released a Limited Collectors Edition. Some of the notable differences are a steel case instead of the regular plastic case and an extra disc which contains artworks of environments and stages including Locust that never made it to the game. The disc also contains a time-lapse on the creation of the "Emergence" mural. -wikipedia