I don't know many people who have not played the game on one format or another, and I've played it on most. The gameplay itself is almost on a par with big brother, and the slight variance to the PS2 version in-game story, retaining the map gives you the feel that you've been here before.
The multiplayer option increases the shelf-life yet further (or until the next one comes out) and adds even more pleasure to your GTA:VCS experience, quite literally will keep you playing for hours.
In the future, there will be an extension pack for your PSP enabling longer life and a much more comfortable gaming position. The much needed relief this would bring would be welcome - but as this is more likely just wishful thinking, my slight discomfort does little to hinder my opinion of a great portable addition to the GTA series.