First of all, let me say that I'm a huge fan of the franchise, started playing when the Witcher 1 Enhanced Edition was released, since then I've read all the books twice and replayed Witcher 1+2 several times each. Witcher 3 is the epic conclusion to Geralt's story (but hopefully not the franchise).

The graphics are simply stunning. Yes, the game doesn't look like some of the early trailers, BUT all the gameplay trailers CDPR released up to half a year prior to release accurately depicted the final product, and anybody expecting any game to look like 2-year-old trailers is at least very naive. So this is not the "bait & switch" or anything some people made it out to be, you knew exactly what you were getting prior to release and the final product looks AMAZING. I can confidently say this is the most beautiful game I've played so far. The game had me literally go "wow" in some places (Kaer Morhen for example), some of the textures like leather on some armour, fur etc look photorealistic almost, the weather effects are amazing too. This is the first game where I literally enjoyed just riding and exploring the landscape, watching a storm move the trees or the sun go down. Yes, there's also some textures that aren't so amazing, but don't forget this is an open-world game and the overall graphics are the best we ever got to see in a video game so far.

The soundtrack is the most beautiful I have ever heard in my almost 20 years of playing video games. It will be hard to have sword-fights in future RPGs without missing the intense Slavic singing. The "main theme" is also grandiose and gave me pure chills when I launched the game for the first time.

The combat is decent. Nothing special, but also very servicable and most importantly FUN. You have your standard fast and heavy attacks, dodge, parry/riposte, your Witcher signs and bombs and now also your crossbow, which mostly serves to bring flying enemies back to the ground or apply bleeds to enemies via one of the special bolt types (which is very useful against higher level enemies, since bleeds are percentage-based).
The alchemy system was totally changed from Witcher 2. At first I hated it, but after getting used to it, I must admit it led to me actually using potions I almsot never used in previous Witcher games (like Thunderbolt and Blizzard). Instead of crafting each potion every time, you just craft (and upgrade) them once and then they are always replenished when you meditate and have at least one strong alcohol in your inventory. Potion length has been extremely reduced from previous Witcher games, so it takes a while to get used to it. Lore-wise Witcher 2 was most accurate when it came to potions (you could only drinke them before combat and they lasted a long time), gameplay-wise both has it's up- and downsides. In the end, after I got used to it, I actually kinda liked the new alchemy system.

Now to the most important part in a Witcher game, the story:
What can I say, the attention to detail in the adaptation is just amazing. You can tell from the major to the minor details that the writers care A LOT about the source material. Now, the games may not be canon, but that doesn't change the fact that they absolutely feel like it. You meet many characters Geralt already knows from the books, like Dijkstra for example, who still has a bum leg from when Geralt broke his knee in the books. You will also meet many other characters from the books I won't spoil here, but most importantly, we finally get to meet Geralt's true love, Yennefer, after CDPR shoehorned Triss into Geralt's life in Witcher 1+2, and boy is she awesome! I guess, if you've never read the books, you will not fully understand how much they love each other, but armed with having read the books twice, the first meeting with Yennefer in the game sent literal shivers down my spine, perfectly accentuated by the amazing soundtrack, you could feel how Geralt held his breath.
The main story, revolving around Geralt's child of destiny - Ciri -, is purely epic, and for me, this is the best writing in a video game so far, especially since the depth the characters have is not limited to the main quest, but actually many of the minor NPCs have more backstory/depth or are just more interesting than even the main characters of most other modern RPGs (and games in general). All the side-quests are handcrafted, you don't have ANY generic fetch-quests (yes, there are fetch-quests, but they're so well hidden inside good and interesting stories that I can't remember a single one as being a "fetch-quest"). The world is beautiful and if you explore you might find an interesting detail or random encounter.
The downside is that the open-world controls feel kinda clunky at times, especially when you can't grab onto a ledge you'd think you easily could reach, but which wasn't intended as such by the devs apparently. This can get frustrating at times, but it can be forgiven seeing as this is CDPR's first open-world game. The riding controls usually feel very smooth, unless you even meet the slightest cliff or hole in the road, then your horse will simply just stop (making jumping over those a pain at times), and Roach also can't swim.

I've not had any major crashes, except for display driver crashes which have disappeared after the latest update from NVidia, so I assume that was on their end, not CDPR's. Other than that I have not had any major technical difficulties with the game, apart from NPCs sometimes "popping in" a bit late, but I blame my CPU which doesn't meet minimum requirements. Apart from that I get a good average 60 FPS with everything on Ultra on a GTX 980 with hairworks enabled (and optimized a few days after release).
The only really annoying thing are the loading screens, which give you a short summary of the point in the main story you're at at the moment; they take a bit too long, because of that.

As for game-length, my first play-through took me about 170 hours and I still have some points of interest left on Skellige (one of the major areas). However I took my time and if you rush it you can complete it much faster, but why would you?

Overall, despite it's minor flaws, The Witcher 3 is definitely my favourite RPG to-date, maybe even my favourite game in general. I give it a 10/10, but I highly recommend reading the books and playing Witcher 1+2 before starting it. Especially the books make some of the scenes MUCH more emotional, thanks to knowing how much certain characters mean to each other.