Just finished the game (vanilla only, no mods or expansions), and I have to say I had a great time. Very few games have done sidequests as well as the various witchering quests in this game. It was really cool to do the PI kind of figuring out what happened to people, and piecing together these interesting and tragic stories (even though the gameplay of that often ended up being holding right click and spamming E).
Obviously there were still several negatives that people have mentioned countless times through the thread. Popamoleizations and MMOizations were pretty annoying, though it looks like most of them are fixed by that School of Roach mod that I'll have to give a try. The one that can't be fixed by mods though is the stupid quest compass. I tried turning it off at the start but it's just so obviously designed to be needed that I gave up and played nearly the whole game following the compass from one place to the next. The worst part is that they built this giant and beautiful world for you to explore, except thanks to the quest compass design, while you're going through the world you're spending half of your time looking at the minimap not really taking in the world they so carefully crafted. They basically shot themselves in the foot with this design. It's hard for me to grasp the fact that the Morrowind school of direction design is used by basically nobody anymore. The real genius behind Morrowind's directions, apart from being more realistic since people in the real world actually give directions by using landmarks and stuff, is that it made you pay attention to the world. To find the landmark the direction-giver told you about, you have to be focused on the game world, which lets you notice how handcrafted and detailed it is, instead of taking your focus off the world every couple of seconds to look back at the minimap to see where you need to go. Of course, you also get the benefit of getting lost, finding yourself in a completely new place, and going "fuck it, guess I'll do stuff here now" and almost forgetting about the old quest, which I always enjoyed.
Immersion can be a silly buzzword when used by stupid faggots who don't know the first thing about it, but in big, well-crafted open world games like Witcher 3 it's actually a big deal. It's still a great game, but it could have been so much more with just one design change.