Final paragraphs from an extensive review that starts here
"At the end of the day, the Surface Book feels like a device that was kept secret. The secrecy was great for the unveiling, since there were only vague rumors of such a device to be announced at the Microsoft devices event in New York, but that same secrecy has, I believe, led to superb hardware being let down by immature software.Final Words - The Microsoft Surface Book Review
And then there is price. The Surface Book is not an inexpensive device. Microsoft is playing at the very top of the market with this offering. Prices range from $1500 for the base model with Core i5/8GB/128GB, all the way up to a staggering $3200 for a Core i7/16GB/1TB/GPU model. That’s a lot of money for an Ultrabook. The NVIDIA dGPU alone is a $200 upgrade on the Core i5 model. You can easily get a more powerful system for less money, but when you look at the high end it’s never a linear relationship of cost versus performance. The Surface Book offers some of the nicest hardware in any detachable convertible. I think despite the price Microsoft is going to have customers for this. The question is will they get the bugs sorted out. The first firmware update fixed a lot, but there are still too many outstanding issues to recommend the Surface Book at this time."