Ebook: Teach Yourself: Improve Your German

Teach yourself is a series of language learning courses produced by Hodder & Stoughton. It has courses in all the major languages and also some of the less spoken or ancient ones. It has not only traditional courses but also others for improvement or learning scripts.

Among strenghts of these courses are: systematic approach, explanations of grammar.
Weaknesses: The claims of CEFR level goals need to be taken with a grain of salt as more vocabulary and additional resources are usually needed to reach them.