Let's not become like the folks over at the GTA forums with all the name calling and everything, gentlemen.
Anyway, when I first heard about the map fully being open right from the start I also thought that was a bit of a letdown. But later I thought it is better this way. I always found myself not really enjoying the game because I was constantly thinking about 'whoa I can't wait to see the other areas of the map' and rushing through the game because of this which is a shame of course. That's not how you enjoy a game. And with the new multiple protagonists approach, it would be silly to not have the map open right away fully from the start. Besides, that the map is fully explorable from the get go doesn't have to mean that you can indeed go everywhere right away IMO. Maybe certain little areas, roads or other things are still closed off for some time in the beginning. Who know.
All I know is I can't wait for this game. Finally the country side is back and it it's going te be huge if all the stories are to be believed. Awesome. The colors look very good as well. Not as grey and boring as GTAIV anyway. Can't wait to go exploring. In some of the previews I read that while Franklin was parachuting, you could see people fishing, people racing against each other on ATV's or bikes and even a park ranger driving somewhere in the mountains. Woohoo.