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