Well, the book arrived and I've just finished reading it. I've got around 10 years experience, 7 of them as a professional, and I found it excellent! Very very useful for intermediate-to-veteran level designers to clarify the whole process of level design into a well organised, structured process.
I'm mainly self-taught and learned through reading around, experimenting and getting tutorials from people I know, so I have this whole jumbled mass of experience and knowledge. It was nice to be able to see it all written down in an organised way that made sense and was stimulating, because when I talk about level design myself it's usually just a discussion about a particular facet. Level design is so broad that although I have very comprehensive knowledge myself, it can be hard to pass it on. Now I own a good book that I can point people to 
I think the areas of the book that I strongly agree with from experience and would like to re-iterate are the importance of thorough planning, the importance of balance and harmony between all the elements, and the most important thing of all - for the final product to be lots of fun to play! 
I definately recommend checking it out 
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