@Anil,
There are many... There are game changing things like Upgrading Nano suit with some awesome utilities (ability to see bullet's path from the origin, etc), to tiny little changes like power sliding when uses use Run+crouch combo (just like Splinter Cell conviction). Gun play feels solid than before. But the big disappointment is, Trees. They look fantastic. But when we shoot them, they stand still unlike the first game. I tried from pistol to rocket launcher and Tank. nothing happened. But i played only one level for a brief period of time. All i can say is, it seems that it has improved in every aspect.