A Guide for the Perplexed
If you are not familiar with the series Guides for the Perplexed then you have a real treat in store. They are published by Continuum and are a clear, concise and accessible introduction to philosophers, authors and subjects which can be challenging.
The books concentrate on what makes the subect difficult . They explain key ideas and guide you to a thorough understanding of what you might otherwise have abandoned as beyond you (if you are like me, anyway).
Adorno: A Guide for the Perplexed
Kierkegaard: A Guide for the Perplexed
Above are just two examples but if you've ever struggled (and failed) to fathom something or found a thinker or subject incomprehensible, it is definitely worth checking to see if Continuum have a Guide for the Perplexed on that very topic. These books enlighten and illuminate without patronising. They are a great resource