Part of the continuing fascination with the Crusades is due to the belief that we are still fighting them, that they precipitated a Christian/Islamic conflict in which we are still caught up. Truth tends to be much more complex and multi-layered than myth, which is indeed why we prefer the latter. But if you would like to get at the former, Tyerman's book is a good place to start. The most important lessons are to do with scope and context. The Crusades were much more than a series of military expeditions by Europeans to the Holy Land, they lasted for far longer than the two centuries we usually credit them with, and the wars between Christian and Islamic nations had older and deeper roots. Nor are their consequences widely understood. As this book makes clear, the Crusades had far more impact on Europe, and far less on the Near East, than is usually thought.
This Very Short Introduction is actually a reprint of Tyerman's hardback Fighting for Christendom (used, cheap copies of which, at the time of writing this review, are still available on Amazon, so you might want to check that out). One consequence is that, at over 150 pages, it's longer than most in the series. Also, I think they must have simply shrunk the illustrations to fit on the page, so that you need a magnifying glass to read some of the maps.
The early chapters give an excellent overview of the subject. The later chapters, examining the impact and significance of the Crusades, and being therefore more interpretive, are somewhat heavy going at times. The author's style is good, but may be slightly too academic for some readers. And he is occasionally prone to colourful moral judgments, such as when he talks of Himmler's 'historically illiterate ghouls' relying on 'rancid imagination'. I may well share this view, but I will arrive at it myself, thank you very much.
This remains an excellent introduction to a hugely important subject, and is a worthy addition to the series.