Call of Duty 2's most subtle ingredients are its amazing weather effects. You'll chase Nazis through pouring rain across bombed out cityscapes in Caen, France, inch across deadly snow-covered trenches on the Russian Front and hunt down Rommel in North Africa's scorching heat. This realistic weather sets the stage both visually and sonically, transporting you to another time and place.
The health system also adds to the immersion ... to a point. As you take damage in the game, your vision fades and you start to breathe heavily. Finding cover and staying put for a few seconds regenerates your health fully (similar to Halo). This allows you to fight on without having to search distractedly for health packs or med-kits. Though it does keep the pace humming along, that superhuman ability feels out of place and distracting in an otherwise hyper-realistic WWII-era shooter. It also gives multiplayer matches an unusual feel, though increased weapon power in multiplayer balances the regeneration system somewhat.