Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
In my working life, I have encountered "Agile" three times. The last time was at a startup based in Oakland. It was Scrum, it was imposed from the top, a tool was introduced first in order to do agile tracking and planning, none of the actual technical practices were ever seriously considered. In short, exactly the kind of sham that Wiliam complains about. It had zero benefit.
Before that, we had two groups at BBC News Interactive starting to do their respective interpretations of XP. One did the simplest thing that could possibly work, for example never getting around to ever putting in the database, and did that in a test-first style. It didn't do standup meetings, paired at times, and every once in a while did a planning game. This team replaced a system that failed almost every single day and had abysmal performance using a 12 computer setup with a system that had two failures in 3 years, performed 100-1000 times better using only a single machine. The second team did standup meetings and planning games, but never managed to implement the technical practices such as TDD or DTSTTCPW/YAGNI. This team failed to deliver and the project was canceled/reset.
Finally, I first encountered what I would now recognize as XP before I knew that XP existed. Hard core YAGNI/DTSTTCPW, mixing pairing and working alone both organically and usefully. We introduced unit testing later and I became an immediate convert, having been responsible for shipping this product for some time and feeling the uncertainty over the question "when will it be ready". I later discovered that a bundle of these practices that we as coders had discovered for ourselves were known as XP, and I eagerly learned what I could from their experience.
So is Agile a sham? Maybe the dadaist manifesto put it best: if you are against this manifesto, you are a dadaist!