I found this book rather heavy going, but that is partly because a lot of the more distant history stuff is of little interest to me. I did, however, also find the writing style a little dull.
To be fair, it is very ambitious in scope and provides a breadth of coverage, not just in terms of timescale, but also subjects e.g. linguistics, economics, anthropology etc that is not available in any other texts that I've seen. It is also extensively referenced. For these reasons, I've given 4 stars, despite having not particularly enjoyed reading it.
I am primarily interested in more recent history and, fortunately for me, this is delivered to near perfection in the fantastic 'State of Africa' by Martin Meredith.