Providing an introduction to the linguistic study of African languages, the orientation adopted throughout this book is a descriptive-structural-typological one, as opposed to a formal-theoretical approach. Formalisms are not eschewed per se but rather are invoked when they aid the central thrust of the book, which is to describe and characterize the languages of Africa in a succinct and concise manner, and to make the facts accessible to the unfamiliar reader. To say that the approach is typological means that a given structure is compared to structures of the same type (typically ones familiar to the readers), set within an established range of variation, and characterized as usual or unexpected. Further detail is also provided, where possible, in terms of the structure's synchronic distribution and diachronic origin. The text assumes at least some knowledge of language structure on the part of its readers, but nothing beyond that acquired in a first-year linguistics course. The book
George Tucker Child's AN INTRODUCTION TO AFRICAN LANGUAGES, published by John Benjamins in 2003, presents the unique and peculiar features of this region's languages. The book is accessible to undergraduates, but it does demand prior courses in phonological and morphological theory and a willingness to follow references (Childs keeps things generally simple, but he'll pique your interest with lots of citations to theories too detailed to go into in this book).
The book covers the entire continent, not just Sub-Saharan Africa, but North Africa as well. It falls roughly into five parts. This first discusses the genetic grouping of African languages, with a good overview of the polemics and the major figures. The second portion is a look at the phonological peculiarities of African languages, such as click sounds, vowel harmony and insanely complicated tone systems. The third portion is morphology and syntax, covering e.g. Afro-Asiatic's non-concatenative morphology. The fourth part concerns typology, while the fifth part is the sociolinguistic aspect. The book comes with a CD that is very useful to really understand the phonology.
My own field is Indo-European, Uralic and Altaic linguistics. I found Childs' book an accessible and entertaining introduction to the interesting features to be found on the African continent, and I certainly learnt quite a lot (talking drums!).