I would give this game a 9.5. It's not perfect, no game is, but it's above it's competition in basically every way.
I'm playing on hard (Blood and Broken Bones) on PS4, about 35 hours in, so these are my impressions so far:
+ scale (probably not the biggest game on the market, but it's easily the most complex and dense)
+ visuals (the best looking open world game i have ever played)
+ seamless world (love the lack of loadings, and the ability to see interiors and exteriors through windows and doors)
+ story, lore and characters (believable world with many mundane stories, brilliant pacing and intriguing characters)
+ no invisible walls (due to the open nature of the world, the ability to swim and the addiction of a jump button, you can basically explore any place)
+ unpredictability (as opposed to the schematic nature of Ubisoft games ['you picked 3 treasures out of 30', 'you climbed 1 tower out of 10', etc], in The witcher 3 everything seems random and natural.
+ exploration (again, due to it's unpredictability, exploration in TW3 couldn't have been more misterious and rewarding)
+ Sound (amazing OST, sound effects and voice acting)
+ content (insane amount of content)
+ gwent (for the first time in my life, i see myself investing hours on a game's minigame)
- several bugs
- loading times (they are too long, gladly there are few of them)
- Portuguese subtittles in Brazil but not in Portugal? Seriously???