(Full disclosure - this review is part of the Books for Bloggers program)
In its unfinished form, I give this book an easy 4/5. I expect that when this book is finisshed that it will be a book I consider required reading for anyone in the development world. Yes, it's that good.
Even though most developers would probably prefer the thrill of software development in the startup world - no cruft, just being able to get things done, typically we're in the "real" world. We work for organizations with a few hundred, or a few thousand developers. Often these organizations have become juggernauts - a huge, overly complicated beast that's nigh-impossible to control. But Lean Enterprise gives us hope. It gives us a taset of what could be. It could be nice if they had a few more prescriptions - do this and you will be able to fix this problem - but they don't.Instead they offer the basic principles that, if you can get your management to agree to will help your organization adopt more agile practices and throw off the shackles of legacy software development. Sure, you may not start developing all your apps in angular/backbone/node/ruby/python or whatever the latest and greatest new awesome technology is, but Lean Enterprise will help your organization move to a place where development isn't such a hassle.
If you want to be an agent of change in your organization, you owe it to yourself to get this book.