Headshots/Backstabs/Critical Hits

I would like to see Headshots/Backstabs/Critical Hits implemented so that you're required to do more than just aim in the general direction and spam your attack. Headshots would be for ranged attacks, Backstabs for melee.

As for armored enemies, you could make some that take, for example, 0-10% damage up front, but take 150-200% damage in the back. This would also open possibilities for tower builds to counter these if the heroes are busy, or the heroes will have to take care of them when the towers can't.

This is a neat idea, especially with the armour unit suggestion. It would also be cool if crits ignored a percentage of armour, rather then just dealing more damage.

However, I personally feel that the different kinds of characters should have different ways of inflicting crits.

The huntress should have headshots, but the Apprentice? Doesn't seem like a mage thing to do. The Apprentice could force crits by fully charging his secondary attack. The Squire would just have a standard, random % to crit, and the Monk could maybe crit on a jump attack or something.

It would be cool that enemies would have weak spots. Some armored enemies have some areas not covered, some get hurt more from back/head etc.
Random crits would be a bit pointless.

I don't want DD2 to become borderlands. I'm, at the very least, reluctant to embrace back stabs for sure. I'm less convinced about critical hits but I'd rather not see the term "head shot" used in-game.