New Features..

 Multiplayer
 Multiplayer Clothes
 High Definition Graphics
 Changed Vehicle Physics (I bought GTA 4, not Microsoft Driving Simulator)
 Improved world detail
 Euphoria Physics engine
 TV (watch once and you're done. Wasted useless feature)
 Internet (read once and you're done. Wasted useless feature)
 Different minigames
 Comedy Club/Cabaret shows (watch once and you're done. Wasted useless feature)
 Can pick up and throw things (even if it is only like 7 things
 Expanded on cell phone idea from previous GTA

Missing Features..

 Silencers on Pistols
 Stealth kills with melee weapons
 Stealth while hiding in shadows to avoid being seen
 Dual-wielding handguns/submachine guns
 Ammunation
 Ammunation Mini challenge
 Flamethrower
 Rampage side-missions with certain weapons
 Buyable Properties
 Parachutes
 Free-fall control of character when falling off high buildings or helicopters
 Extensive Clothing Options
 Car Customization
 Car Color Choice
 Police on motorcyles/ police motorcycles
 Nitro
 Airplanes and Jets
 Air dogfights against military jets
 Jetpack
 Aircraft hanger/helipad to keep Planes/Helo's
 Garage storage for cars (there are houses with WORKING garages. no excuse)
 Tanks
 Military
 Combat Helicopter that can shoot missiles
 Working Semi's W/ Trailers
 Farm Equipment
 ATV's
 Trucks with ramps to carry cars, ramps cannot be lowered to use as stunt jump ramps
 Flight School (no planes in GTA 4.....so..)
 Helicopter school
 Driving School
 Multiple Races w Car Rewards
 Marathons
 Bicycles
 Melee training system, kung-fu dojo, boxing arena, etc...
 Mountains & Country to have large chases or fun with vehicles
 Tatoos
 Haircuts
 Monster trucks
 Stadium for monster truck, demolition derby, or dirt bike racing
 Diving Underwater
 Paramedic side-missions
 Firefighter side-missions
 Truck side-missions
 Cheeta
 Something do spend money on
 Cannot enter Police stations
 No gang territory battles
 Cannot conquer Liberty City
 Katana sword
 Machete
 Chainsaw
 Working Forklift
 Saving your pictures you take with camera
 Dunebuggy
 Hovercraft
 Tractor
 C4 explosive charges
 Brass knuckles
 Tear Gas
 Golf club melee
 Fire extinguisher
 Thermal Goggles for night-vision
 Cannot drive Trains
 Home Burglary
 Weapon skills improve over time. If you use AK a lot, you get Hitman rating with AK, etc
 No gangs attack you for crossing their territory like in all other GTA's.
 Remote control toys
 Gambling on horse racing, blackjack, etc
 Less variety in single player mission. GTA 4 missions are the same from start to end
 Niko cannot climb as advertised by Rockstar
 Gym/customizing your character's body shape (fat or skinny or muscular)
 No zombie/riot pedestrian mode
 No cheat for cars fly
 No cheat for jumping higher
 No cheat for boats fly
 No cheat for running faster
 Cannot pick up vehicles with helicopter