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?

One tactic I used frequently was instead of opening the door and opening fire, I'd stand in front of the door, fire a couple rounds to alert everyone and use the door as a funnel of unadulterated, massacring death.

@bluefoxxy said:

One tactic I used frequently was instead of opening the door and opening fire, I'd stand in front of the door, fire a couple rounds to alert everyone and use the door as a funnel of unadulterated, massacring death.

This is how I was finally able to get the "Just Plain Luck" achievement of killing 3 guys with one thrown brick. Still took a ton of tries to get it just right, though. And if anyone is curious, it was in the first room in the second floor (from the staircase on the right) of Push It (level 6 I think). This also required me to intentionally get killed a bunch of times on the first floor until a brick spawned in the back room.

Map the Restart button to W, A, S or D (I picked W), so you don't need to move your fingers to a completely separate button in order to restart the level.

This might be an exploit, but I don't think bullets can harm you when you are in the middle of executing someone.

@Leptok said:

This might be an exploit, but I don't think bullets can harm you when you are in the middle of executing someone.

It's true, but the problem is, once you've finished executing someone you're probably just going to get killed.

@Leptok said:

This might be an exploit, but I don't think bullets can harm you when you are in the middle of executing someone.

It's true, but the problem is, once you've finished executing someone you're probably just going to get killed.

@Leptok said:

@BeachThunder

@Leptok said:

This might be an exploit, but I don't think bullets can harm you when you are in the middle of executing someone.

It's true, but the problem is, once you've finished executing someone you're probably just going to get killed.

Unless they shot all their ammo.

This isn't something I would go into a situation relying on or expecting, but it has certainly saved my ass more than a few times (especially when the other guy has a sawed-off shotgun).

That actually reminds me of another set of tips (exploits?) that may or may not be useful for anything other than artificially boosting your score.

1. You get points every time you knock an enemy over, but only if they're carrying something at the time.
2. As far as I can tell, enemies with empty guns cannot do anything to hurt you. Period.
3. Enemies holding empty guns don't have the common sense to drop them and pick up different weapons.
4. Unarmed guys seem to grab whatever weapon is closest to them, even if it's an empty gun.
5. When an enemy is hit with a thrown weapon, the thing that hit them usually seems to land closer to them than whatever they dropped.

What this all means is that individual enemies can be rendered completely harmless by flinging empty guns at them. What's more is that you still get points for punching them in the face, since they're still technically armed. Repeat as needed until your score is as high as you want it. (I spent way too much time trying to get A+ ranks on all the levels)

This game is truly difficult

press space bar when enemies walk close to walls and you can execute them through walls