5. Everything's a weapon
Normally, there are two ways to get a weapon in Grand Theft Auto. The first and cheapest way is to start a fight with a cop and steal his nightstick and gun. The second is to go to an Ammu-Nation shop and pick from a slowly unlockable selection of firearms. That's just not going to cut it anymore - if you're in an alley and some angry Yakuza catch you low on ammo, flailing around with your fists until you're lying in a pool of blood is going to make for a less-than-enjoyable experience. But there might be another way - what if the alley was packed with weapons, just waiting for you to snatch them up?
Above: Screw running scared for the nearest Ammu-Nation - if a fight breaks out, we want to bust heads with whatever's handy
It's not like it's a farfetched idea - Dead Rising did it with its mall full of makeshift weaponry, and Rockstar's own The Warriors enabled players to grab hunks of wood, bricks and bottles off the street to inflict pain. Seeing as that was recently done on the PSP, it probably wouldn't be too hard to weaponize whatever garbage is lying around GTAIV's environments - or even to use it to sneak up on your attackers, Manhunt-style.
As long as we're dreaming, how about filling the world with smashable objects, and then letting us pick up the pieces to use as weapons? In a pinch, making your own shiv by shattering someone's window could be a resourceful way out of a deadly situation. Also dumb and self-destructive, but that's part of the fun.