Beat the game on Hard with High Chaos back in 2013. I focused heavily on stealth and tried to be a good guy by avoiding killing guards. I killed thugs and plague victims without mercy though, and anyone else I considered a bad guy. I used Dark Vision almost constantly to find treasure and observe the movements and vision cones of enemies, striking when the time was right. Most often choking the guards out and hiding the bodies. Possession 2 was quite useful for dealing with tricky situations where I could not take someone out without being seen. Of course sometimes I screwed up and was forced to kill guards. I did not use many tools. My goal was to incapacitate every enemy, fully explore every level and find all the loot. I used Bend Time 1 for combat vs multiple enemies for the times when I screwed up, and headshots with the wrist bow when fighting enemies I did not care about killing.
I loved this game; loved the setting, atmosphere and story. The gameplay is excellent though I will admit that killing everyone is far more fun than being non-lethal. Without Dark Vision, the stealth would be obnoxious. I was disappointed when I finished the game because of getting the High Chaos ending despite not killing many enemies. I might as well have butchered everyone. All my effort put into choking out guards and hiding them was wasted. In my opinion, the biggest flaw in this game is the lack of intermediate chaos stages between high and low.
I played The Knife of Dunwall (Hard) afterwards and went full High Chaos killing everyone. If I am not going to get credit for granting some enemies mercy, then I might as well kill everyone and have more fun doing it. I also have the City Trials dlc, but did not care for it; too arcadey and not enough deep immersive story.
Years later I purchased the Bridgemore Witches dlc and beat it on Hard in High Chaos. I used Void Vision 2 almost constantly and favored sword assassinations. Also did wristbow headshot assassinations. There were plenty of times where I botched stealth and used gun and explosives, though Bend Time 1 was the best way to deal with multiple enemies.
Corvo’s powers: Dark Vision 2, Bend Time 1, Blink 2, Possession 2, Vitality 2, Agility 2, Bloodthirsty 2. Spent points on others but did not use them.
Daud’s powers: Void Vision 2, Bend Time 1, Blink 2, Vitality 2, Agility 2, Bloodthirsty 2, Pull 1. Never really used Pull and never got Summon Assassin.
For both characters, I favored simple charms that improved health, mana, movement speed and combat ability. I felt it was too much of a pain to swap out charms to optimize them for a given situation. I did not use any of the corrupted charms. I spent my money on favors to get runes and charms, and useful upgrades. I generally did not favour improving consumables (such as ammo capacity) and went for more permanent upgrades.
Definitely want to play through the entire game again on Very Hard. I probably will not try to do a Low Chaos, 100% non-lethal or ghost run.