As prase and David Gerard have said, to understand QM, first learn QM. The actual mathematics and physics of it, not any popularisation. When you can pass a finals exam in the subject, with distinction, making minimal use of reference materials, then you will have reached a position from which you may be able to begin to participate in useful discussions about QM. How many similarly qualified people there are on LessWrong to have such a discussion with, or who they might be, I do not know. I hasten to add that by that standard, I am certainly not one of them. I do not know QM. I hope I have never pontificated on the subject here or anywhere else, but I certainly do not do so now. Anyone wanting a quick self-test, and with access to a university library, might entertain themselves with this volume, a book of exercises in QM, with worked solutions. If you can do even one of the problems at sight, and get it right, then you know more QM than you will ever discover from popularisations. When you can do all of them, you can claim to know QM.

I think the expository part of the QM sequence can be skipped without significant loss of understanding of the broad philosophical point EY is attempting to make. However, if you are interested in QM for its own sake, I would recommend reading a quick non-pop-sci introduction to the theory before reading the sequence. Otherwise I think you will emerge from the sequence with only the illusion of understanding. In my experience on this site, it is far too common that people whose main exposure to QM is the sequence misunderstand not just the mathematics of the theory but also the conceptual structure of MWI. If you want a really good, really short introduction to the mathematics of QM, this book is excellent. It's written in a very engaging, non-textbooky way, so don't worry about it being a dry read. It does presume some mathematical sophistication though. If you're not comfortable with differential equations and linear algebra, I would advise against reading it. If you don't have that sort of mathematical background, read this instead. It actually is an introductory book, presuming very little knowledge on the reader's part. I recommend it over standard intro textbooks (such as Griffiths) for someone with your interests, because it focuses on developing a deep conceptual understanding of the theory rather than on doing calculations. Finally, you could try David Albert's idiosyncratic but compelling book on the philosophy of QM. Again, the book is completely introductory. It won't teach you much about the math of the theory (for that, read Hughes), but it will give you a short overview of the main extant interpretations of QM, evaluating their strengths and weaknesses. The author is skeptical about MWI (in fact, he seems skeptical about pretty much every interpretation), but he's a very sharp philosopher, and his arguments are worth considering seriously.