Straight forward tactical shooter
Typically you just use your teammates a lot to go out in front of you and kill off all enemies. And if they fail, you can step in and finish off the rest easily as the enemy's locations are now known after the firefight. If your team mates are killed, you can easily revive them and they will auto-heal if they just get wounded a bit.
This makes the game feel a bit like an RTS, where you control two super soldiers who will be able to clear out almost anything for you. Once you get used to this playing style, you will feel a bit like you are cheating, and the game becomes rather repetitive and linear. Only when you play without your team mates you will feel some pressure.
However, the extraordinary graphics makes it a joy to play and the graphical diversity is a great motivation for diving further into the story, which by the way never gets in the way of the action. It is always delivered while you are playing.
The city scene is amazingly realistic, and I especially appreciated the soft shadows and great view distance. You can see miles and miles... Unfortunately the cities lack realism in the form of civilian traffic. You will never encounter any cars or people in the streets, it all feels like deserted ghost towns. Only really noticeable as the graphics otherwise is so amazing.
The maps also suffer a bit from the hidden maze syndrome. Which means you get the impression you have a lot of freedom to go everywhere, but in real you are inside a camouflaged maze where there will be some cars parked in a way that will exactly block your way in that direction or other objects making up the "wall" in the maze. This hinders your freedom, but also stops you from wandering off and getting lost.