What the forget are you talking about? The only thing unrealistic about it is the health system. No game has a realistic health system.
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So I assume you rush into huge warehouses full of armed men and kill them all, drive into people all day, outrun the police by walking into a building, and lots of other over the top bullstuff on a daily basis?
If so, why do you need to play GTA IV?
Also, the "realistic" driving they implemented in GTA IV is really bad.