I played through the game once whereby I did it non-lethally, for the most part as I accidentally killed a guard by letting him roll into the water and also killed one out of shock along with a few weepers, and want to do a high chaos playthrough to experience the other ending. Since I also completed my initial playthrough in a mere 12 hours, which is admittedly missing a considerable amount of side-quests and other content since I purchased the game and had only 1 free weekend where I wanted to see the ending and fate of Emily, I also missed a lot of stuff that will be easy to explore without being constrained to not being lethal. However, I don't want to just be playing this as an action game and still want to do stealth, so is this possible? I heard a reviewer state that high chaos is only possible if you go around killing everybody in plain sight - is this true?

Not true. You can be an unseen assassin kill everyone and still get high chaos. Thats how I played when I did a high chaos playthrough.

Sniper/ ninja assassin playthrough- that is probably how I'll do my high chaos game. All those jump assassinations should be fun.

I'm doing a mixture of stealth and straight out attack on my current high-chaos playthrough. I don't want to get myself into too many group fights until I unlock more powers but I'm killing every enemy I see.

Such a different gameplay experience so far too compared to my previous 2 playthroughs.