It successfully improves from the first.
I was expecting to be underwhelmed because of the closeness of the releases of both GRAWs and it got me thinking of Call of Duty 3 all over again.
I first went online and beat all of the online campaign with others and I couldnt have been happier with the greater challenge it gave me over the co-op campaign from GRAW 1 and I was happy with the new weapons. (Rx4 Storm all the way)
Then; I started the single player.
OMG. This is where you do a double-take, the graphics are so life-like that I was sweating from the Mexican heat. At the end of the first Act, at the part where I got to call a jet to air strike on a tank that was 100 ft in front of me I just fell in love. The explosion effects where of the big-budget-hollywood kind. It was so nice that I just turned off my 360 right afterward so I could do it again.
Among the other improvements that I found nice are the:
-clan support (ala halo2)
-full screen cross-com (single and multiplayer)
-fun achievements
-good combination of small and large multiplayer maps (all in lush detail)