If you do everything in the campaign, including the Gwent side quests, Races, Treasure hunts, Witcher Contracts, and exploring all the maps, I'd imagine you're looking at no less than 135-140 hours. I've skipped out on Gwent(which could really add up some hours), most of Treasure hunts, and have no intention of exploring all the question marks on the map. I figure that's how most will play it(other than skipping Gwent), and I think I'll top out at around 100 hours. And that's without the two rather large DLC packs. It's a gigantic game, that isn't really artificially lengthened either. Even the basic side quests are meaty, including the monster hunts, and usually have two or three sequences to them. It's easily one of the most impressive games I've ever played, in terms of always doing that little bit extra to make every little thing matter, and not just feel like mindless busywork or grinding.
As for comparisons, it pretty much stands alone. It takes elements from all sorts of games, and puts it all together into it's own unique package. It's hard to pin it down to anything in particular. At it's core though, it's a third person open world action RPG, with tons of exploration, missions, and decision making.
I'm going to stay up to stupid hours, aren't I?
