The biggest issue with most evil routes is that they simply remove options from the game without much in the way of pay off.
I do not want to simply kill everybody that my character comes across if I decide to role-play a more morally challenged character. The individual in question may not even be outright evil, just callous and an opportunist.
On the other hand, if a particular antagonist has nuance and/or charisma then I believe there should be an option to defect and work with that character.
I'd argue that modern fantasy is so bland, in many cases, because it assumes that the player wants to be the 'good guy' at every possible turn.
