I've never heard a bad review of them, I think that's the most striking thing as most chess books have at least a few detractors out there.
One advantage is that it's kind of a one-stop shop. Many club players (in my experience at least) waffle back and forth between books and training methods, never really making any progress. With the Yusupov series, if you can stay focused, you don't need to waste time looking at anything else or wondering *what* to do. You just put your nose to the grindstone and do the work.
Another advantage is that it's essentially the classic soviet system of chess training and has been proven time and time again. Yusupov is one of the greatest trainers in the world, he himself was trained by Dvoretsky and went on to collaborate with Dvoretsky on training materials. So you could not ask for a better trainer. Essentially you're getting 24 2-hour lessons (per book) with one of the best trainers in the world for the price of a book, where else can you find this kind of value?
Really the only disadvantage that I can think of is that, it may seem like a magic bullet to chess improvement. It's not. The magic bullet is hard work. The Yusupov books are just one way (a really good way) to enable you to work hard on the right material. If you buy the Yusupov books thinking it's an easy way to 2200, then you're in for a rude awakening. The material is great but you do have to work very hard.
Also you really get the best out of it if you can dedicate ~2 hours per session to studying. Each lesson is self-contained and designed to take that long (more or less), and while it's possible to split the lessons up into two sessions, I really wouldn't recommend it. So if you can only afford 30 minutes or so for your practice session, it's probably best to just do some tactics and endgame puzzles rather than working a quarter of a Yusupov lesson.
You do have to study these books with a physical chessboard -- true learning is best achieved through experience and he makes it very clear that if you're just passively reading the book, you're not going to get the best out of it. I certainly agree with him so I do not consider this a disadvantage, but you may if you want a book you can read on the train without a set in front of you.
The writing style is fine. They are very active books, and keep you engaged. You will spend a lot more time moving pieces around on a chessboard than you will reading.
I found the orange books to be challenging (in a good way) at my level (1400-1500 on here). There were a couple of lessons that I "failed" and had to re-do but overall I didn't think the material was above my level.
I highly recommend them for the very motivated student -- with the caveat that I haven't really looked at the blue/green books too much, but I expect they're just as good as the orange ones.
Build up... Boost... and Chess Evolution (the 9 chess workbooks).
What are your impressions of these? What are the main advantages and disadvantages? What level did you find each book to be pitched at? What was the writing style like (Dry / casual / boring)?
The 9 books are on offer as a hardback set from Quality Chess. Wondering if they're worth looking in to.