Hearing him speak and the books...
I feel his overall tone and modesty mirrors each other, he responds and speaks well. To me, what he has written feels very consistent. Among his books that I finally read are the Thoth, the one on Alexander Crowley (new) and My Life as a Magician.
I like knowing where Duquette is coming from on Crowley, and his books intermix seriousness with humor and clarity when he can. There are some fun personal notes that make for more lively reading in his books.
I read the Qabbalah book by Duquette off and on, and it does have great detail. But it's just my taste, I seem to be more of a Gareth Knight fan when it comes to an overview of certain concepts...
Mari H.