Very short and very well-written, this little tome tells you probably all that can be definitively known about Chaucer--which ain't a lot, and perhaps speaks of this book's length. I'd just finished Ackroyd's definitive biography of Shakespeare, which is a lot longer, though not as long as his biography of Dickens, which totals more than 1,000 pages and can be used as a weapon.
Ackroyd has a breezy but classical tone, which means you feel like you're learning something from a guy who's comfortable with his subject, and who knows a lot about it, because he's researched the hell out of it, and added a good deal of common sense when necessary. This is different from, say, Bill Bryson, who's even breezier, and who also knows of what he speaks, but who comes across as more Wikipedia learned, if you know what I mean. In his defense, he never testifies otherwise, and seems to be trying always for an intelligent breeziness. He evokes incredulity more often than common sense.
At any rate, this book brings Chaucer the man and his courtly jobs--of which there were a great many--to life, and it evokes the Middle Ages well. If you want to know a little bit about London, circa 1370-1400, here you are. Chaucer exclusively comes to light in documents of the king's court and of the legal court, and that's it, as he and his Canterbury Tales became famous after he died. He wrote much more than the Tales, and was known for his long poems, but apparently only in the king's court. One of his duties, the book attests, was to entertain the court with them. They seem to be made for performance, and for print, in turns. Weird.
He was a contemporary of William Langland, and his Piers Plowman, and of John Gower, so we're really going backaways. Canterbury Tales seems newer than that, which speaks of Chaucer's urbanity, another point of Ackroyd's. When the few writings of the time were about farmers and rural folk, the Tales was about the London that Chaucer knew. I often feel like the Tales, in its frame structure, could be emulated today, so it seems new, despite its age.