Donald Keene's "Seeds in the Heart" is the first of his 4 volume History of Japanese Literature. This one covers the works from the beginnings of the said literature till the late sixteenth century (Momoyama Period). The other 3 are about literature of the Edo period ("World within walls") and the post-Meiji restoration pieces, with 1 volume for prose, another one for the rest ("Dawn to the West").
Keene's book is an authentic Tour de Force, and arguably, the best History of the Japanese Literature that anyone who reads in English can access. This first volume include a stagering 1200 pages of essays and work, and cover in a very high (and sometimes, detailed) degree the main productions of the literature of the times: from Heian diaries, Imperial Anthologies, Prose Romances, Renga... You name it.
The scholarship is very well done, and yet the book remains very readable and enjoyable, with lots of excerpts and explanations. Information on translations is also ubiquitous.
In conclusion: if you're interested in having a detailed and well written summary of Japanese literature in English, this is were you'll get it. The only criticism I can make of the work is, perhaps, that the author clearly judges Japanese works from the standpoint of Western aesthetic discourse (privileging for example 'depth', 'subjectiveness', 'realism' and 'originality'). I totally share this stance, but I imagine there's others who wouldn't be so happy with it.