First of all, I like the Witcher 2. So now that that's out of the way, I'll continue:
1)If someone doesn't like a game you like, realize that THEIR opinion doesn't actually detract from YOUR enjoyment of it. You really don't need a whole group of people agreeing with you that something is great for you to enjoy it. You CAN enjoy things that other people (or even MOST PEOPLE) don't like! Yeah! And here's something that you might find SHOCKING: Other people can dislike things that you like! I know that's a bit much to handle all at once, but it's the truth! Really!
2) Believe it or not, some people might not like the same things you like for legitimate reasons.
3) There will always be negative reviews of games. No game has ever received 100% positive reviews. If a game is good, then you don't have to be "worried" about bad reviews "destroying" it.
4) At the end of the day.... it is just a game.
Young people (10~25, and I'm in that range), especially these days, haven't experienced much of life. We are sheltered, for the most part. Those who have the money to afford video games have a pampered, privileged existence (I count myself in that category). To be blunt: we're emotionally and intellectually immature, for the most part, trying to form identities for ourselves.
Most people, rather than looking within for an identity, choose to look outside themselves, at pop culture. They latch on to certain genres, console platforms, developers, etc, and they start to identify strongly with those products. Rather than see these products as.... just entertainment products (which is what they are, just products), they see them as a critical part of their identity and lifestyle. When they see or hear someone attack a product that they have incorporated within their identity, they feel as if they are being attacked as well.
It's a childish reaction. You are not a game. Criticism of the game is not criticism of you. If you enjoyed it, and someone else didn't, please realize that they are speaking negatively about the game, not you, and that their negative experience doesn't somehow invalidate your positive experience. It's psychology 101, people - you need to realize the faulty emotions that go on within your brain, so that you can control those emotions and fight them.
Then there are those people for which Video Games are their entire life. They have few (or no) friends, they have no other hobbies, they don't really do anything except play games, think about playing games and earning money to play games. Usually these are the younger folks, still in school, who don't have to worry about jobs and stuff. These games make up a big part of their life. Trust me, I've been down this dark path. They derive such satisfaction and emotional wellbeing from the game (because they don't get it from anywhere else) that they start to almost worship the game as a source of happiness. When someone comes along and says that they don't like it, it's almost like they are being told that their "religion" or "lifestyle" or "life philosophy" is wrong, and they react very negatively do it.
To sum up: Defensiveness comes from two things:
1) Emotionally immature gamers who invest WAAAAAAAYYYYY too much emotion into the franchise because they don't have anything else to care about (like careers, family members, spouses, high-ideals or, in general, life)
2) From people who incorporate the game/developer/product has part of their identity. Attack the product/developer/game, and they feel as if you are attacking them and their choices. It's tribalism 101.
Reflect on your emotions - you know what I've said is true. I like games. I play games. But I have a career, an education and a life outside games. I have a proper perspective. Games are ONE part of my life, but they are NOT my entire life. If someone criticizes a game I like (and I like the Witcher 2), you know what I do? I do the mature thing: I simply don't care!