Anyone who has spent time trying to complete all their Combat Knife challenges will tell you that knifing in Black Ops II is the worst it's ever been. In an attempt to eliminate the issues people had with enemies lunging 5 feet or getting clean OHK with their knife on players who weren't even in the same area code, Call of Duty went a drastic route in tighting the hit detection of knives. While I don't disagree with the intent, I feel that there was a major feeling of "all or nothing" with the Dev team. It seems they felt that you either made knives near useless or they were going to be as lethal as a katana (a weapon that should be considered for Ghosts).
To add some quick background, the combat knife should always be an equipable weapon and you do this by holding the Triangle (PS) or Y (XB). This is the only way you can knife unless you're using the Balistic Knife.
Here's a brilliant solution to knifing to both nerf and buff some aspects:
1) The lunge needs to be realistic, in Black Ops II there's about a 6inch reach your player has. This doesn't get the job done and leaves players slashing 3 or 4 times to get a hit. There needs to be some logic in their movements. If an enemy is lying down the player should have the ability to knife in a downward motion, if the enemy is off center the player should have the logic to lunge in that direction.
2) When sprinting players should have a bit more of a lunge than when you're standing still. I think there's a bit of this in the current system but far too often when I'm hunting someone down I'm having to be right on their heels in order to land a hit.
3) Animations can aleviate the anger players have in how pathethic some knife kills look despite being a OHK. With the Combat Knife you're given two possible attack; brutal and quick. Quick attacks are done by pressing R1 (PS) or the right trigger (XB). Brutal attacks are done by hold both L1 and R1 or the left and right trigger.
4) Brutal attacks give you bonus towards your score. They take longer and leave a player valnurable during the attack, they look much more intense, and are quiet attacks. A brutal attack from behind will have you grab the enemy and stab them in the chest, carefully dropping them to the ground. From in front, a brutal attack is a two handed downward stab to the chest that instantly kills the target. From the side it's you grab your target, turn then aroud and stab them in the chest.
5) Quick attacks are fast and are used when you need to take out multiple enemies. The disadvantage of it being quick is that you earn a standard amount of points and the stab is messy and loud showing you on radar. Quick attacks from behind are a throat slit that leaves the enemy moaning inaudiably, from the front is a abdomen stab, and the side is simply a side stab. Though they are still OHK, it's a little better than a whimsical slash that often doesn't show you hitting your target in the least.
DEFENDING A KNIFER
6) Unlike other titles there are ways to protect yourself from a knifer. First and formost if you're shooting a person they're movement speeds are reduced greatly and the knifer is not able to lunge nearly as far even when sprinting. This leaves a knife kill impossible unless you're enemy is right on top of you.
7) If you're jumped by a knifer you can break away by clicking the right stick, much like killing a dog in Black Ops. However, the window isn't very big so you have to be fast. Also, all you're doing is breaking away, you're not inflicting damage.