Over the course of the game, I've been noticed a few details that may or may not be useful for you. But for what it's worth, they generally helped me. Also, some of these may have been introduced in one of the more recent patches (either that or I just never noticed them before)
- Hostages actually have 2 potentially significant uses. First is that you run like 30% faster while you've got a hostage, for whatever reason. Secondly, they can take a few bullets if you use them as a human shield. However, if you do this, the hostage will die and you can't move until you drop them (which takes a second). You can still pivot, and I think the body still blocks bullets, but you can't move anywhere.
- The knife is just fast enough so that holding down the attack button makes you just about immune to melee attackers, assuming you're facing the right direction. Most (maybe all) of the other melee weapons take longer to swing, so holding down attack constantly is dangerous due to the potential for enemies to run in between swings.
- You normally can't shoot guys that have been knocked to the ground, but there is an exception. If a guy gets knocked into a wall, so he's sitting propped up, you can still hit them.
- The drill execution no longer gives an absurd amount of points, sadly.
- Throwing the knife sometimes knocks guys over, but sometimes just kills them. I can't tell if it's a random chance or what.
- Whatever weapon you're holding when you go from one floor to the next is what you'll be holding every time you respawn on that floor. This can be useful for trying to get some of the weapon specific achievements for rare weapons, like the brick.
- You can get away with a lot more than you might expect with a knife and the chameleon mask. For example, the guy carrying a shotgun at the end of the hall on the second floor of Crackdown? He normally starts shooting at you before you can even see him. With the chameleon mask, you can run right up and stab him in the face before he realizes you're there.
That's all I have off the top of my head right now, but are there any tips you guys have?