The Witcher 3 is best summed up as the character driven story and production values of Mass Effect, the massive open world and quests of Skyrim, and the randomness / horsey of a Red Dead.
The Witcher 3 is massive, you could easily write a book on the design and development of this game. It is very easy to see how the developers came up with the 200 hour claim to complete all the quests. It's not exactly the sheer quantity of Skyrim but it's very close, and each element has an incredible amount of detail and uniqueness that Skyrim was missing.
One thing that kind of initially threw me off was the scope of the main story. The bulk of it is a quest to find two missing friends. This is a bit weird given the epic scale of the game and it being the last of a trilogy, you would expect a giant war or Game of Thrones like competition for power. But that all comes in due time, much like one of the best games of the previous generation, Mass Effect 2, the story focuses on characters and their individual stories.
This is where Witcher shines, every character you meet isn't one dimensional, they all have back story, flaws, and behave in interesting and believable ways. By far the best part of Witcher is the choices you make, they are interesting and have meaning on both a large and small scale. Coolest of all every choice is not black or white, there is no good choice or bad choice you just decide and face the consequences. You will face choices of all kinds, mostly involving the lesser of two evils. Even when a decision is clear you have to decide the severity of punishment someone deserves, or if everyone involved is lying to you which they often are. These choices don't immediately jump out as consequences either, they may or may not come back to bite you in the ass or you might have ruined someone's life and you would only know it if you went back and visited.
Combat is something that they have improved upon over most RPG"s as well. It is not quite Batman or a dedicated character action game level but it is dynamic and engaging. Enemies all involve different strategies, you must account for different weapons a person useless, the weaknesses a beast has, the magic needed to defeat a witch, etc. This is all left up to you to discover. Just as Mass Effect implemented a fairly solid third person shooter into an RPG, Witcher 3 has solid sword and magic fighting mechanics.
The visuals are also a large draw for me to the Witcher 3. The game has a crazy amount of detail, every building, item, tree, farm, character seems to be unique and expertly crafted. The quality bar is also never lowered, even side quests that you could easily miss have detailed cutscenes, unique mechanics, and animations and match the production values of big main quests. Unlike some large games that seem outsourced and separated, in The Witcher everything works in cohesion, there is a very focused effort to all the models and mechanics. Every moment of the game is so sharp, the weather effects, soft lighting, and modeling, impress more the longer you play.
If you are looking for a large game with interesting story lines, Witcher 3 is for you. It's not without some open world and RPG roughness, but it makes up for in the best production and gameplay mix of any big scale RPG I have played yet. Plus rarely are games good enough to include fetus monsters, suicide, alcoholism, nudity, and batman detective vision all in one quest.