I recently completely completed The Witcher 3, including both expansions ("Hearts of Stone" and "Blood and Wine") and all of the trophies (Playstation Trophies, not Monster Trophies... though I probably got all of those too). There are probably a few minor things I haven't done and I won't have seen every possible combination of options but I feel it's sufficiently completed.
I did enjoy Blood and Wine, it's much better than the first expansion. The story is quite good, although it feels like it sidelines a main character who seemed to be important initially ([spoilerinline]Dettlaff[/spoilerinline]) by making their fate feel like a secondary concern to everything else. On the plus side, it gets major bonus points for having a great buddy character for Geralt to hang around with. My favourite moments in the main game tended to be the ones where Geralt is working/spending time with a friend and the best part of the other expansion is similar too. Geralt is a pretty interesting character anyway but I think his friends often bring out the best in him (or at least different sides of him) and they're generally pretty interesting themselves (even Lambert... well maybe not Lambert).
Blood and Wine also does a good job of giving a sense of closure (especially if you've completed the main game already). There's a nice message in the end credits relating to this being the last game that will star Geralt (not necessarily the last Witcher game, I suppose, but we'll see) and it does feel like the end of an era, in a way.
Overall it really is a great RPG. Plenty of fun sidequests (though not all are equal), a solid story, an interesting world and some great characters. The downside to games like this is that they're a pretty big time investment and it's not always easy to focus on just doing the best bits. I think it's well worth the time and effort, although I do wonder if I'd come back to play it again some day. That's often the problem with games in general though, there are always new games to play that build on the successes of the past and it can be difficult to justify the time to play something older.
