After finishing the campaign last week had time to think about what was happening with Cortana a little bit.
The first thoughts that come to mind are straight forward, “Cortana has turned. She doesn’t seem to care her actions resulted in many human deaths.”
However, I wouldn’t be surprised if there is more going on than we saw (which in turn might change the opinion of some who didn’t care for the campaign).
Perhaps she is being controlled in some way by the Didact’s network, and its either a forced version of her, or not her at all. Or maybe she is attempting to gain the guardians trust to make an attempt to stop them, although the latter would be less noble.
Or she could just be the typical AI going rouge story we have seen in other works such as iRobot but I definitely like the introduction of Locke.