People called him pretentious because the fact that this video is his opinion is not made obvious. I saw the video and disagreed with several of his opinions, but pretentious is not the word I'd have used to describe it. To me, pretentious means that one thinks that one is better than one actually is in some fashion, the most common factor(s) of superiority being intelligence or importance. Do I think that he managed to present his opinions in an articulate manner and brought up legitimate reasons about why he does not like the game? Of course I do. He was right about certain things. But his other arguments were, admittedly, more like things that he had against the game personally that he could not overcome. For instance, his main argument was that the game was too slow. I never grew up with the game, mind you, so there should be little nostalgic influence here, but I do not agree with him. The game certainly isn't fast, but slow is the wrong word to describe it. His own impatience, which I have observed in his Game Grumps videos, certainly was a factor in his calling this game slow. Another thing that he didn't like that I disagree with is how linear he believes the game to be. This is another result of his impatience, and unwillingness to read dialogue, which can once again be demonstrated in Game Grumps, in his utter disregard for any sort of instruction given in a game. But not what I would call "pretentious".
Wow, that quickly turned into a rant. I apologize for that. But, in case my point wasn't clear, as I'm sure it wasn't amidst my ramblings, is that while I personally do not consider him to be pretentious, his opinions make it seem so, as some of his problems with the game are more personal than others and people call him pretentious because of it.