After 20-odd hours, I'm giving Witcher 3 a solid "B". Looks nice, I like the general world building (and like that there's actually weather), combat is fun if somewhat repetitive (roll behind, whack whack whack, roll behind whack whack whack) and the conversations are usually interesting even if the voice acting can be uneven (the children are terrible). Most of the major characters are interesting enough to want to talk to them. I like that monster levels aren't dynamic so you can bump into things that eat you in two bites. The character progression system is good.
The "open world" nature is really more "follow the linear main plot and pick up ? marks along the way". The quests largely boil down to "Hold down your M2 and examine/follow the red glowies". Crafting feels like a mess and I'm a walking hardware store of twine, wire, wood, leather scraps, cloth, bits of metal, paper, etc not to mention the flower shop I keep in my pocket. Merchant sold recipes don't say what level the gear is for so I've no idea if I should drop 65 gold on them or not. Looting 50,000 sacks and boxes with one spool of string in each is tedious. As I said, combat is fairly repetitive and I don't see it changing up much beyond getting more use out of signs as I level them up.
It's a well done world but actually playing the game hasn't really hooked me. I play it for an hour or two then feel done for the night. I can see the quality behind it but it's not a world I feel myself lost in.
Personally, I give it a solid A after about 20 hours. I'm enjoying the world, the size of it, and the enemies. You can even fight a level 12 monster with a skull and win, at level 4ish. I'm playing on hard, and I don't find combat that repetitive. I also don't roll, almost at all. Using the bestiary, signs, dodges, parries, oils and potions makes combat a lot less repetitive. Although yes, some fights still are repetitive (such as golems).
As for the linear main plot... that's not how I'm playing most of it. I've been exploring a lot just to uncover the map and finding signposts. You can also do a lot of quests out of order, which happened to me.
I've also been trying to role-play a little, treating Geralt as neutral good (though he's probably supposed to be more neutral).
Equipment crafting is a mess though, and mostly pointless. You mostly just want to craft the treasure hunt (Witcher) gear, unless you want to waste money.
You also don't -really- have to loot most boxes. I do, just cause I've always done so in games.
The only objectives I've found like they probably should have left out are the monster nests. Those are very repetitive and pointless.
Exactly how I feel...also, the horse riding is horredous and the responsiveness of the character and horse outside of combat is "slow" or "laggy" (not sure how to describe it). Looting is another gripe. You have to be at a certain angle and right on top of it to loot.
I like the horse riding. Combat on the horse though, not so much. And when you're moving slowly, it is very "laggy" feeling. And the looting thing is an issue -- you get the prompt to loot, but it won't loot cause your camera isn't facing it.
I also read a lot of the lore before starting, like everything I missed in the first two games. The story is a lot more interesting once you know how the first two games led to Witcher 3. Also helps a tiny bit if you know a little bit about the novels, just so you're more involved in the secondary characters.
One thing that annoys me (shut up, I'm playing the GOG version) is that there's no way to take a screenshot. Those glorious Keira breasts? Much better than asshair.