Echo everyones view that the respawns were a pain - Wipe out a checkpoint, drive 200 yards down the track, turn around and go back, and they were all alive again. This was tedious on missions where you had to pass through the same area a couple of times.
But the positives - big world, plenty to do, plenty of different ways to do it.
Atmospheric, in so much as the passage of night and day were good. And when everything around you was burning, and you could hear the crackling of wood and dry grass, and almost feel the searing heat from the flames as you surveyed the destruction you'd just caused, it was fun...
So personally, I liked it!