Best in the world? Depends on preference (Sorry guys).
As far as RPG's go my favorites are open world, which falls along Fallout, and The Elder Scrolls series (As far as all the main entries). The Witcher is more linear with your world restricted to maps of around a few square kilometers at a time, which there's nothing wrong with that, some people like games with a sense of direction and progression, though my progression personally got lost with my insistence on side questing, and confusion/frustration when I got stuck without the ability to progress, most of which started in the second chapter (I consider the fort area in the beginning to be the prologue chapter), I will share a few thoughts however.
The Witcher 1 from what I played so far (12 or so hours) found me a bit stuck. There's a lot to do in each chapter, but it means a lot of exploration and experimentation. For example, exploring to find magics, trial and error to mess with alchemy and ingredient hunting, leveling, balancing leveling and questing between two types of swords, magic, alchemy and extra skills (Combat boosts while drunk, anyone?) I probably should have started in the beginner mode to start and went on to normal, but then I still fell into the trap of looking everywhere in everything ever to collect every single object I could possibly get hold of and storing them like a single chipmunk in control of a bank vault. There's also a ton of things in the world that require gold, of which you'll never get enough to buy everything in the world (As opposed to Fallout 3, Morrowind where you can end up with so much money that you can construct houses out of your bottle cops/gold coins) so it's worth thinking about what's important to your playthrough and where to focus skills and stats early on. It's also worth exploring around and saving often if you can. One last thing to keep in mind, you don't have an infinite storage, it's akin to Diablo where the things you pick up take up space, and that space is represented in area of your inventory. Weapons however HAVE to be stored on your person among the 6 or so weaponry slots, so if you're killing people and selling their weapons, hit the stores immediately when you can as items don't stay on the ground forever, and since you have precious few spots to carry extra swords and axes and knives and torches and so forth, if you don't plan on using them you might as well sell them as quickly as you can.
The Witcher 2 I don't know much about, it'll probably be 3 years before I have a computer that can handle it so I can't help you much there. Either