I enjoyed this more than I expected. This is very much a novel of the form, "competent people solve science and engineering problems. In Space!", which is not really my thing. It didn't help when an obvious villain was added to the mix, or that characters who moments before had been hard-edged political realists ignored this villain long enough for the villainy to become a problem. The 'seveneves' concept was strained, and really, if I'm going to read about a future society like the one in the book, I'd rather someone better at 'soft' science fiction was writing it. And too much of the second part was a travelogue through the amazing engineering of the world of tomorrow.
But most of it I enjoyed. The science and engineering in the first half was clear without getting bogged down. When it works, I do like some science fiction in my science fiction sometimes (and it's always flattering to be convinced you understand what's going on :) ) What was happening on Earth was handled well, the characters were not deep but were at least distinguishable, the drama was dramatic, and the whole thing just moved along smoothly, which is a big consideration in a book this size!
Best novel of the year? It's always difficult to compare novels which do different things, and this is a book with a one-track mind. It gets a place in my list of nominees, so far at least.
Edited to add: This is getting pushed down my list of potentials, not by another novel, but by some non-fiction - An Astronaut's Guide to Life on Earth. While I knew Stephenson had his finger on the scales, its very difficult to mesh his depiction of life in near-future space with Hadfield's.