I'm getting it to see what else they've changed. I've read a fair bit about it and some of the things sound fairly cool to pass up.
1. No loading screens after the first one (SA loads when you enter a building)
2. ATM's and mobile phones that you can actually use.
3. Climbing power lines
4. The new cars and physics engine
5. Size of the map (which is comparable to SA in terms of area)
That's all I remember off the top of my head.