So the most powerful power I believe it is dark vision. Yet, it uses up practically no manna and lasts a long time. Do you guys use it a lot? I find it to be overwhelming. So, I decided to stop using it except as a last resort. I have found the game to be much more enjoyable this way. I feel that balance wise, it should use up three fourths of your manna and be something that you have to think hard whether or not to use. As it is, you could pretty much go through the entire game with dark vision on. I hope no one does this because it destroys the beautiful artwork and also the tension of the game.
Another thought for those complaining that there is no new game plus. Try playing the game without dark vision, or any of the other powers for that matter except for blink of course. Totally different experience.