Got it last Friday.
While I don't think it's the masterpiece that many call it, it's what a good gta is supposed to be like. It's much more varied than IV (which got boring after a while for me). Story and characters are great. The extra activities are nice, though I only enjoy the racing and (strangely enough) tennis. The hunting and hanging out with friends don't strike me as particularly fun things to do, but then again I haven't tried them enough. I haven't tried golfing.
The map is big, but much of it is only vast wilderness, fun to ride in and do stunts with your buggy and quad and look at, but not much else (It's a good world to incorporate DLC missions, i think). I'd have liked if there was another city, not only Los Santos.