Without a doubt the best RPG I've ever played. The open-world atmosphere is unparalleled, all of the characters are interesting and have their own stories to tell, missable side-quests could very well be part of the main campaign, the addictive "Gwent" card game should be its own standalone game, and the systems it implores are plenty and very deep.
I rarely ever go off the beaten path in open-world games, but I found myself completely ignoring the main quest because the side activities felt so meaningful. The world CDPR created is downright gorgeous, and you can tell they hand-crafted a vast majority it, as it truly feels like an interconnected world. Despite talks of a downgrade, the game is a stunner. I often find myself stopping to just admire the surroundings. The world itself doesn't revolve around you, and will continue to move on without your direct intervention. There's a lot more going on than what you see and experience. You'll see trees swaying, the weather constantly changing, animals and monsters milling around, and caves and hidden areas filled with treasure, and all of them combine to create a very convincing world. Also, the facial animations are top-notch, and make the characters feel alive. Never have I seen such a wide variety of expressed emotions in a video game characters before. It's astounding.
Like the Witcher 1 and 2, what makes this game stand out is its lack of black and white decisions. No matter what you choose, your decisions will have consequence whether that be a positive or negative, and this is what makes the world feel so compelling. The completion of side-quests linger after you play, and some are even connected to the main plot. The side-quests don't feel like throwaway quests, and the characters you encounter are all intriguing.
Combat is actually very enjoyable despite what others have said, and truly shines when you master the mechanics. You have a variety of tools at your disposal: parrying, dodging, signs, bombs, potions, crossbows, and of course Geralt's Silver and Steel swords. Like in Dark Souls, enemies have predictable movesets, so dodging out of their way comes down to proper timing. However, I found myself fighting with the camera especially in larger groups, and Geralt's animation can be a bit unpredictable, but it's fun being able to look in your bestiary to find out what the monster is weak to and to prepare accordingly.
Gwent is also the best mini-game ever. It's a card-collecting game where you'll challenge over NPCs. Its mechanics are simple to understand, but here's a lot there to master as well.
Performance is also a hit-or-miss. I found several areas where the FPS dropped significantly and parts where stuttering grew to be a minor issue. However, none of them proved to tarnish the overall experience, and I'm sure will be fixed with future drivers and game patches. You won't be encountering load screens as often, and even when you do, they're short.
All in all, one of the best games I've ever played and the best RPG I've had a chance to try. At first, it may feel overwhelming to be introduced to so many different systems as once, but when you get the hang of it, it all gels together. It's a very long game, and you'll without a doubt need to set aside time to finish this quest.