I see now I have a bit different view than most people here, so I’ll try sharing my experience. The question is, what’s important to you:
A. Polished cinematic set up and experience.
Then W3 is deffinently the winner. It is much more polished, scenes set up is like in movies, combat is pretty blockbusterrish. In KCD it feels like you’re seeing amateur theatre most of the time. However, the cutscenes are sometimes pretty decent and dramatic.
B. Pick your own decision.
You probably lose with both games. In both the main character has it’s character already - and you mostly choose between minor shades.
However I felt like in Witcher 3 you may take a bit more heavy decisions on consequences. You choose who you support and what’s entire country fate would be. In KCD freedom is only for how you achieve your character goals. Sometime I was pissed off that I have to choose options that are idiotic to me, because there are no others.
C. Fun action gameplay.
To me, Witcher 3 is much-much more tactile fun. Despite all critique to it’s gameplay, I actually love it’s combat one of the most in games. I like that you can dodge (and I mean dodge, not just roll out) pretty much any atack, and constantly dancing between dodging and putting hits in right moment. I don’t find it too easy as well. Unless you fight underlevelled enemies OR have mastered the gameplay, quests do give you some challenge (on normal difficulty). And afterwards you just set it to max difficult and almost every foe kills you in two successive hits, so you better make it perfect.
With KCD this aspect isn’t a thing at all. You don’t feel cool while making combat. However, there are good parts. It’s more skillable - you really have to master everything before it works. So I guess the accomplishment feeling afterwards is MUCH higher.
D. “Choose your path” gameplay.
Limited in both games. In W3 you are first of all a monster slayer. Your main tool is a sword. Fencing is the key. I don’t think you build a proper tank either. However you add magic to it - it’s pretty powerful and does change tactics. And potions, of course, put some variety to gameplay. Anyway, you won’t build a ranger, a thief, a pure mage or anything else.
With KCD it’s same and different in the same time. Speaking combat, you use melee. There is a bow, which you can win some battles with - but there are no skills for it and it’s very hard to use. But most of the time you can really avoid direct combat. You can use stealth to nock down enemies, poison their food and so on. You can use dialog skills to pick paths that don’t lead to combat. You can’t avoid combat entirely though, but at least it’s one of the least combat-forced RPG game I’ve ever played. Which I personally love.
For some reason one of important parts of an RPG for me personally is ability to live inside the game world. That means I want to be able - and to actually need to - sleep, eat food, return home to get some rest from quests and travels and so on.
And I must say KCD is one of the best game ever for those rutines. You have energy and hunger, which punishes you if you don’t pay attention to them. You have to do lots of things which aren’t adventurous - like constantly repairing your clothes, washing yourself, following recipe manually when brewing potions and lots more. Even saving is connected to actual in-game actions, like drinking shnappes or sleeping in a safe place. I love those little things, but for others it might be a chore.
W3 doesn’t do that almost at all. What you’re left with is eating to gain health regen (which I appreciate, though), meditating to recover or to wait for some exact time and… is that all? Even brewing potions doesn’t have usual amount of small manual steps - you only make each type of potion once and then it autorefill when meditating unless you need to upgrade the potion to a new level. It only keeps the fun parts, but for me personally that decrease immersion.
Not sure, I’ve covered all the aspects I can think of… Probably will continue later if I come up with something else.