1. Effective use of violence.
This is one of the few games I know where the violence really feels necessary or appropriate. It helps ram home the nature of the environment and situation. Also, the fact that your so close to the enemy a lot of the time, it becomes much more personal. I have to admit, the gun battles feel much less appropriate though. I think its the fact that enemies don't drop down fast enough. If they were wearing such heavy armour, I would have expected less blood. It's only a minor point however. Also, in gun battles, it isn't made apparent in any tutorials that you can use cover.
2. Believable close combat and stealth.
I'll admit the AI can be dumb at times, but the transition between close combat, stealth and shooting was always very smooth. The stealth system definitely isn't the best in the world, but felt great, especially how they used the heartbeat as a proximity detector. The use of eyeshine felt natural for these sections and you even had the time when you got really close and turned it off to avoid being blinded. Pretty sweet.
The close combat just worked. It was really simple, but it felt really visceral and required a bit of brains and timing to be really effective. As mentioned above the violence was highly effective. Also, since it was common to kill the enemy quite quickly, it felt really lethal, especially with all those counters and finisher moves.
