This looks suspiciously like one of those management BS books, that take you 200 pages to tell you what you already know. It could quite handily and effectively be dismissed as such, except that sometimes the obvious stuff still needs a little formalising, and the guy who wrote this is a bit of an expert.
I'll take a step back. What's this book about? It's about changing organisations. Duh. Interestingly, though, many failing organisations would rather go on failing in the same old way than address the obvious issue, and challenge themselves to do something about it. The difficulty of big change is always underestimated. So, most of this book is about engendering a sense of urgency, building up momentum, etc.
Moreover, the title is very deliberate. The author emphasises that change comes from 'leadership' - there being someone at the top with leadership and vision and strategy, and some goal beyond things ticking over. Kotter says most organisations are filled with managers, whose aims are to stabilise and standardise and generally control the situations - exactly what you need most of the time, but less useful in accurately steering your straight into a brick wall. He thinks leadership skills are not recognised and fostered enough.
If the book were only given to his apparent intended audience, only a few hundred copies would have been sold, as he seems to be aiming it at the CEOs of major international organisations. However, the ideas involved are relevant way down the chain, to any situation where things are broken and people are in denial.
Having said that, I think the book is still overly simplistic. While Kotter has much experience working with large companies to manage giant change processes, and has identified a process with a list of necessary steps towards huge change, it's not clear that the list is sufficient! Big change is difficult, and I don't think the book is a magic bullet.
Even with these flaws, I think it's an excellent book. It demonstrates the difference between management and leadership far better than anything else I've read, it puts office politics into perspective, and provides insight into what's going on up the management chain.