Almost done, about to take on Radec in the final show down. So far, very enjoyable experience.
Overall, yes, this game feels similar to COD 4. But while I was playing it, it reminded me of these games too:
1. Those flying robots shooting at you reminded me of Halo.
2. The train section reminded me Gears of War.
3. Controlling the robot to take out tanks reminded me of Lost Planet.
4. Mannuing AA gun to shoot the fighter jets reminded me of Crimson Skies (and Ratchet games).
I also like being able to know where I should go by pressing the "up" button, and that remidned me of Fable II, though not directly similar.
It's funny that this PS3 exclusive reminded me of so many 360 games. To me, it is a very good thing because I love all the above games mentioned.