Well GTA3 is supposed to have a better story...
The main character speaks, and there will be like 90 minutes of cutscenes (compared to GTA3's like... 30 I think)...
And with a city at least twice as big as Liberty City, and with indoor areas, I'm sure there will be plenty of new things to discover
Heck, there were a couple small little areas in GTA3 that I didn't discover until owning it for like 3 months... and while it wasn't anything big, when you own a game for 3 months and find a new area of any kind, it sorta surprises you and you're all like "D00D WHOA MAN D00D!"...
Yep...