A lucid, direct introduction to perhaps the most indirect thinker of the 20th century. If you want an introduction to Jung's key ideas this is a great place to start.
Storr has written extensively about Jung, so clearly sees great value in his work, but is more than willing to criticise Jung's ideas (chiefly his obscurity, and also his tendency to see meaningful connections when perhaps there are none). This leads to a really balanced, sober read.
Jung is a strange thinker because his work juggles a handful of disciplines (theology, mythology, psychiatry, literature...). Storr, whose background is in clinical psychology/psychiatry, ties the many strands of Jungian thought together by grounding them in therapeutic practice. It's not that this is inappropriate, but Jung's work is profoundly philosophical and can be valuable to individuals who have no interest in therapy. In many ways, Jung's work was a response to the problems outlined by Nietzsche (especially how to orient oneself in a world which struggles to reconcile science and dogmatic religion). Storr doesn't draw much attention to Jung's historical context, which I think is a missed opportunity.
In short, if you're interested in Jung for philosophical reasons, there are more satisfying introductions (I would recommend Oxford University's very short introduction to Jung). If you are pursuing Jung out of psychologyical interest, this will be a very useful read.