Note: I haven't finished the game.
But from what I have seen, there isn't enough game mechanics to support a evil playthrough. This is not to say you can't roleplay a evil playthough, but rather there isn't enough game mechanics cratering to such a playthrough.
Settlement System - I spend can spend all this time building settlements, but I can't use a mesmerizer to enslave potential settlers. Nor can I sell information to raiders for (reward), so they can sack the settlement. I am largely pigeon holed into being a beckon of hope, if I want to use the existing system. The quest line and dialogue is geared solely for the "good" playthrough. (I just want my own "raider" settlement.)
Questline - From what I have seen here,(note: havent finished game) I'm not exactly given alot of free will on the subject of how the quest plays out.
NPCs - There is to many essentials, its hard to take a kill everyone goal seriously when no one but a few raiders die... (They should have figured I wanted to shoot this guy in the face and adjusted for it.) https://youtu.be/e0E4wviq9Jc?t=420, not that he will die.
In FO3, I was able to:
Spoiler - Sell a child into slavery
- Nuke Megaton
- Bomb the Citadel
- Commit Genocide (side with Eden)
And this isn't really that much, but at least I could get a rise out of 3Dog.
Dialogue - I just wan't to say some seriously evil crap sometimes, not just be sarcastic.
I'm not saying im not happy with the game, I like it so far, but I just want more to cater to the evil side of my toon.