The only leap GTAIV took though was a technological one. In terms of gameplay it was a massive leap backwards from the previous few games.
I'm interested in V only in so far as I want to see if they do an about face on some of the decisions they made in IV. Chief among them being the god awful mini games that you had to do in order to maintain relationships and reap the benefits that came with them. Some more interesting characters wouldn't hurt either.