In a nutshell, I think the Keith Baines translation is an excellent edition for the lay reader, high school student, or first-time Le Morte D'Arthur reader who wants to enjoy the essence of Malory's work. Baines' translation is fluid and makes Arthurian Legend accessible and enjoyable for the modern reader.
Although the Baines edition does lack the style and diction of Malory's Middle English, within its pages you will find all of the characters and events that make Malory's work so rich and exciting: the story of young Arthur and his mentor, Merlin; the treacherous Morgan le Fay, the adventures of Arthur and his Knights, the Tale of the SanGreal(Quest of the Holy Grail), the Fisher King, the tragic Elaine, Launcelot and Gwynevere, and the final battle between Arthur and Mordred.
I use the Baines translation to teach an overview of Arthurian Legend to college-prep. senior high school students (British Lit.), and I couldn't imagine using another edition of Malory's Le Morte D'Arthur at that level. (Of note, excerpts from this Baines translation appear widely in high-school textbooks because it is so accessible).
If you are an advanced student and require a scholarly treatment of Malory's text in Middle English, this is not the edition for you.