This book contains all of Malory's renditions into Middle English of the Arthurian cycle. His English is easier to understand than Chaucer's, and anybody with a fair knowledge of English will understand it. In addition, Malory really does know how to write: we have here a truly riveting read. A wordlist at the back of the book translates most (but not all) terms that have either changed in meaning or are now obsolete.
Unfortunately, this is a paperback. The paper and print quality are not exactly top notch either, although the binding is decent. Thus only 4 stars.
All in all, this is highly recommendable. If you're interested in the tales of Arthur, Merlin, Perceval, etc. then this is a must read.