I bought a physical copy of the Amber Diceless RPG while in Scotland last week, and read it cover to cover. I've heard people talk about it for years, but diceless roleplaying games tend not to be my preference. My main complaint is that most of the ones I've seen (Nobilis 2e, most notably) confuse avoiding a physical randomiser (dice, cards, etc.) to resolve disputes with having underdeveloped procedures of play and mechanics.
Amber isn't really an exception to this, though it's the beginning of this paradigm rather than a latter development within it. It's a bit frustrating still, because the game clearly does care about using procedures to depict specific themes and create certain emotional experiences, but doesn't carry this through consistently. The attribute auction that begins a new campaign is reasonably well-known, and creates a very specific experience (player competition) that is intended to play itself out in the rest of the game. More procedures like this would have been great, and there are a few others, but the game emphasises that its goal is ultimately to have you progress to freeform play.
I know the formlessness of freeform roleplay was lauded during the late 1980s and early 90s, with the idea that rules served as barriers to the imagination being its guiding aesthetic principle, but that underlying principle wasn't true then, and it isn't true now. Rules and procedures and mechanics are affordances, and using them well is about choosing the specific kinds of behaviour, themes and affects one wants to be able to produce. Freeform roleplaying strips away those affordances (this is different than minimalism about rules) with the hope that unconstrained imagination will somehow pick up the slack.
So I find it weird that Amber lauds this kind of playstyle, while it's at its best when it's furthest away from it.
As it is, we get extensive, very well-done, samples of play that seem capable of development, but stop short of being true procedures, because they don't provide clear decision points or criteria by which to select from different choices. In particular, advice on how to adjudicate characters choosing and/or switching which stat or attribute is being compared could be more extensive and standardised. If one is relying on referee judgment as the main means of resolution, then it's important to train that judgment with not just examples, but also maxims and guidelines.
One example of this stopping short is the text mentioning briefly how stats can be weakened or damaged, but never actually clarifying how or why they might be (at least that I could find). Another is the discussion about Endurance (an attribute) being used to adjudicate contests that continue on long enough, without "long enough" being clearly explained. There is a bit of information on whether a contest is swiftly resolved or not, but this is presented unlinked to the prior statements the game made about endurance. The worst of the sting of this is taken out by the examples, but I would have preferred more clarity and definition overall. On the other hand, the various powers are well-articulated, with numerous examples of specific abilities and problems that come along with using them, and truly seem like a useful prosthesis for imagining the world and characters' capabilities within it..
I'm not too enthused about the Amber setting itself, but I thought the book did a pretty decent job making it seem interesting and exciting, and the default set-up does do a great job explaining how the party knows one another, why they associate with one another, and what their relations to the broader world and the important NPCs within it are. The discussion of "sockets" and "plugs" by which PCs fit into adventures must've been pretty innovative when first presented, and I think it's something any referee could benefit from reading. The use of text from the Zelazny series is evocative, and I think you emerge from reading the Amber RPG with a fairly clear idea of the kinds of adventures you could run.
I'm sure this review comes across fairly negative, but I did like the book for the most part. I thought the referee advice was strong and useful, and the game was innovative as heck for its time, and still has a lot to teach any referee about how to handle a table well. Like most innovative and experimental work, it's incomplete and not fully worked out, because it's busy creating a style that other games (Lords of Gossamer and Shadow, Lords of Olympus, etc.) would pick up on and develop further.