The spirit of Vice city, San Andreas, is the ingredient lacking from this game.
GTA 4 leans towards the realism side of things, only slightly, but you will notice it. Niko bellic, whilst having some great lines, is ultimately hard to attach to - unlike Vercetti or CJ.
The Driving is EXTREMELY clunky. This pretty much ruined the game for me.
Firefights are quite good, the cover system is a welcome addition.
There are a plethora of things that will make you go wow, and the physics are nice, if odd-looking.
The police in this are pretty damn heavy handed. kiss your epic police chases and showdowns from vice city and andreas goodbye.
Missions are boring, no more looking forward to the next chapter in the saga and what you would have to do!
Characters arent as great as previous titles.
Get rid of the mobile phone, and people calling you up all the time then being pissed when you cant come in the middle of a mission!
I have heavily compared this to previous titles, but i think vice city had the spirit which, you will realise a few hours into playing this, is not present.
All in all, a well-made game, if untrue to its legacy.