I've never found it dark - just very powerful. It can be dark if you are exploring the dark, and light if you are exploring the light. In that way, it is a truly universal and flexible deck. It's also very beautiful, complex and subtle. Like Aleister Crowley, in fact
To me, it is the result of one of those dream collaborations. I see DarkInquisitor sees it only as Lady Harris's work. That is much more than Lady Harris herself thought. The Thoth tarot is the child of those two great people - a child of their minds, hearts and wisdom, and of their combined energies. That's why it is so beautifully balanced.
I am far from knowing it well, though I had my first Thoth years ago. I stopped working with it for a while, frightened off by Crowley, until I came to read more of his work, and understand where he was coming from, and what he was striving to achieve. When I came back to the Thoth, it was after I had spent many years in close contact with some real darkness - the darkness of war, torture, death and immeasurable loss, the darkness of hunger, rape and cruelty. Having worked to bring about peace, respect and understanding in these surroundings, I have come to appreciate the Thoth as a deck of light - light in a world that can sometimes be so dark. A deck of hope.
Do what thou wilt shall be the whole of the law.
Love is the Law, love under will.
Those two sentences course through that deck - words of love and responsibility. And also this one:
Every man and woman is a star. I turn to the Thoth star card, one of the most beautiful cards ever painted, and I can see my own starryness, and that of my fellows.
It's a magical deck, in every sense of the word.