I don't mean this as an insult to anyone's negative view of the game or how they feel after the ending. But I think the disparity has to do with professionalism. A critical review must be written to certain standards and takes the game as a whole. It should (though they don't always) equally way all areas in which the game delivers, from plot (overall, not just one ten minute cut scene) to acting, gameplay, art direction, music, multiplayer in this case, etc.
A fan/player rating can be "from the gut." If a fan feels hurt/betrayed, they can go and "punish" by leaving a negative review. They have no standard to uphold beyond their own personal ones, and no one is assessing their performance on a professional level. You see this on iTunes games all the time. "This game is awesome, it plays amazing, and it is the best game on iOS ever... but it needs a sequel. 1 Star until you announce this." There is a large disparity with user reviews these days, as people ignore what they liked about a game in order to "take it out" on the dev over one thing they didn't like. They figure it is the best way to get their complaint noticed, since review scores can influence sales.