For the record I do not have Windows 10 yet. I've always been more of a "wait until service pack 1" kind of guy when new incursions come out, and I think I'll be that guy in this instance too. I'm seeing a lot of favorable reviews of Win 10 but also a lot of comments about mostly minor problems but problems nonetheless.
There are tons of reviews out there of course, many that seem to just be blowing MS, but here is about as fair, detailed, and balanced a review as you're likely to see:
Windows 10 review | The Verge