What I liked
It's a window into 14th century England. The cast of characters comes from all levels of society: everything from a nun to a miller to a "clerk" (i.e. scholar) to a "manciple" (apparently, a person charged with managing food provisions for an institution like a convent). It's especially interesting to see how these characters interact with each other in the "framing story" (the events along the journey to Canterbury, as opposed to the many stories that they tell along the way). There were many bizarre ways to make a living back in those days.
Although the book is very religious, it is also critical of religion. There are several stories denouncing religious authority figures for abusing their power.
It's got so many tales, at least one of them is bound to interest you. Topics include: a swindling miller, the virtuous martyr Saint Cecile, a corrupt judge, the Sultan of Syria, greed and betrayal, a bird-whispering ring, the thing that women love the most, and alchemy.
Regarding this particular edition, I like that the editor (D. Laing Purves) translates a lot of the Middle English, but leaves it untranslated when necessary for meter or rhyme. This way, you can learn a bit of Middle English as you go along, rather than being completely overwhelmed diving headfirst into an untranslated version. You'll learn a lot about English etymology. (Middle English explains a lot of bizarre features of Modern English. For instance, the "silent e" at the end of a word used to be pronounced!)
Even better, you can get this e-book free in the Kindle store. (You know you're reading an old book when it has high-quality critical editions already in the public domain!)
What I did not like
Fair warning: Chaucer died before completing this book. You won't get to hear a tale from all of the characters, and a lot of the framing story is missing. Still, what does exist is plenty interesting.
Some of the tales are jarring to modern morals. There's one about "cursed Jews" murdering a Christian boy, and several that joke about rape.
The margin notes format was designed for 80-character-wide monospace text, and is sometimes a bit confusing on the Kindle. It's quite legible once you get used to it, though.
Two of the stories are prose, and the editor of this edition (D. Laing Purves) abridged about half of each of those stories. I was mostly fine with this, except that in the latter story (the Parson's sermon) he cut the discussion of Lechery. I guess, being a citizen of Victorian England, he didn't want to talk about sex. Anyway, you can find other translations of this "tale" online, which I recommend doing---it's quite interesting.