This mod enables player to smoothly go to super slow-motion and is easily customizable from within the game.
There are many bullet-time scripts but I just wasn't satisfied so made this thing :).
It uses .net scripthook and .net 3.5.

Installation:

first you need .net scripthook up and running, get it here http://www.gtaforums.com/index.php?showtopic=392325

then just place the UltimateBulletTimeMod.net.dll in the "\scripts" folder like "C:\Program Files (x86)\Rockstar Games\Grand Theft Auto IV\scripts"


Usage:

default settings are F1/F3 for bullet-time On/Off, to show the customization dialog, open up the console ("~" key) and type "ubt" (+ enter :), in case that nothing happens try alt+tab to windows

cheers

by Nemo

mod homepage:
http://www.gtagarage.com/mods/show.php?id=7718