I was a couple of weeks late buying the game also
Before that I'd only played VC on my nephew's xbox for 5 minutes in '02 and LCS on his PSP in '05. I knew about San An and all the controversies off the news, but I only bought GTA4 because I'd just got an xbox out of boredom.
Boy was it a life changer! I couldn't continue growing veg on my allotment, because I was always thinking there was something better to do in Liberty City. And when looking at that multiplayer option became too tempting, I got myself an internet connection, an xbl account and shortly after a PC.
It really is something great that they build these worlds for us to explore and have fun in. Congratulations on 5 years of awesomeness.