Fenixp: Eh, I wouldn't say so. Baldur's Gate and Infinity Engine games in general were huge because they opened up this obscure, overly complicated RPG genre to wider audience by streamlined mechanics and simple interface combined with DnD ruleset which was still quite popular (yes, there were other DnD games before it, but not as user friendly). On one hand, you can blame them for being at the beginning of massive streamlining of RPG genre, heralded by Bioware. On the other hand, you can thank them for being at the beginning of direly needed streamlining of RPG genre.
Witcher 3 doesn't really share that level of importance, nor is it in any way comparative mechanically. It's good, but I don't think that alone is a sufficient basis for comparison. The reason why you see people comparing it to Skyrim is because it's open world, but I'd say the game from ye olden days which is closest to Witcher 3 would probably be Gothic.
Witcher 3's gameplay is absolutely inspired by Gothic (I believe some of the developers mentioned that). Whenever I enter a cave or building in the game, it instantly recalls Gothic's engine for me, which also streamed environments instead of putting a load screen in your face.
That being said, I wasn't talking about mechanics or historical importance (the only thing we can say about TW3 at this point is that it's the most successful European-and especially Polish-RPG ever (Gothic is sadly overlooked in the U.S.). I was simply talking about having a massive scope while retaining the intimacy and quality of writing that is typically reserved for much smaller, more linear games.
zerebrush: OK, "the old ones" had been in need of a perfectly done plot line. And although visuals in BG had been better then in "The Bards Tale" from 1985, the story had to be a lot more then what you get in some of the more recent titles.
W3 on the other hand: you can spend a lot of time in Velen (true for most any other region of W3), just looking around, being amazed at the visuals, you do not really need the story, just go sightseeing.
And, I really think that if CDPR would not have had some books to fall back on, their plot writing might have been a lot less interesting then what you find in BG, or even the older ones.
So the success of W3 would not have been possible without our actual machines and the basics of some already present stories. The tech behind the machines (and some talented 3D fuzzies) gave us a level of detail that simply could not be done in these older years - and if you look at the success that a game like "Grimrock" seems to get, makes me wonder what will happen next, both in visuals and plotwise.
To the question at hand - no, I do not think that W3 will be remembered in a way that BG is. I still can remember parts of "The Bards Tale", while some things seen/done in Novigrad or on Skellige already are slipping my mind.
I'm not sure I follow. BG was set in the Forgotten Realms setting, designed mostly by Ed Greenwood. Like CDRP, Bioware's BG series borrowed heavily from stories by Greenwood and R.A. Salvatore, and of course introduced new characters, timelines, etc. The Witcher games are essentially sequels to the books from which they get their setting.
It's hard to say how TW3 will be looked at 20 years from now, but I for one will never forget the first time I entered Novigrad. It was the first time I was truly impressed (and overwhelmed) by a city in a game. The questlines utilized the city's setting very well imo.