I think this review warrants a more philosophical analysis:
Short Version:
The way I see it, what makes WoW evil according to Yahtzee and others is that people keep playing it because they're obsessed with slightly improving their character through better equipment. This only becomes a problem when better equipment is considered an intrinsic good, while the actual gameplay becomes a chore. At this point the player is no longer having fun or participating in recreation: they have established something within a video game as a legitimate life goal.
Long Version:
It's one thing to have the desire to prestige in CoD as a game dependent goal (i.e. a goal that one only acts in order to achieve once they have turned on their console), but it is quite another to have the same desire as a life goal (i.e. a goal ranked among professional success and personal relationships). The difference is that a game dependent goal is a goal one has when one is already in a gaming mindset, most people rarely get online because they want to get to that next level; they get online to blow off some steam and getting to the next level is a part of that. There's nothing in the game itself that makes it an intrinsic goal; it's played for enjoyment. But many WoW players have set something WITHIN THE GAME ITSELF as their goal and this goal transcends the realm of the game and intercedes with other goals that most people would consider a much higher priority (e.g. sleep, studying, work, relationships, etc.).
Another word for something that is given unnatural priority is an 'Obsession'. The psychological definition thereof focuses on anxiety, but I'm using the word in its more common sense. Just because these people wouldn't be committed, it doesn't mean that they're perfectly healthy. The way I see it there are two major symptomatic signs of obsession:
1) When something starts to hold such a high priority that it begins to take up an undue amount of the person's resources and the sacrifice of other major goals that would normally be balanced out(e.g. when someone starts losing sleep and meals over something.)The more of the other goals one is willing to sacrifice for something, the more obsessed one is with it.
2) When one loses sight of why one had the goal in the first place (e.g. if someone keeps playing a game for some reason even though it is no longer fun).
When these two things happen, a hobby turns into a perverse obsession.
1 without 2:
If the player still finds the game fun and can't stop playing it this would be a much lesser form of obsession in which the player is at least still getting something out of the game. In fact, this can be even more destructive because in the perverse case where the player is no longer enjoying the experience, this can be pointed out to them and become a strong reason for them to quit. 1 without 2 might be considered a mild form of obsession, but it isn't perverse so much as simply one needing to get one's priorities straight.
2 without 1:
This is really just a mindless habit. 2 is a relatively common occurrence, we lose sight of why we do things all the time. It is worth mentioning in the case of obsession because when combined with 1 it means that a person's motives don't quite match up with their commitment, which, I believe, is the quintessential distinguishing mark of obsession that most people will point to.
So... does this apply to WoW players? More than a few I think. What I think makes WoW prone to cause obsessive behavior is the online community in combination with gameplay that is centered around constantly improving the stats of one's character in small increments. Or numbers if you will.