Cataclysm left a bad taste in a lot of mouths. That's going to color early reviews, and a good number of people aren't jazzed about a number of things, between launch day bugs, rep grinding, and valor gear being locked behind reps locked behind reps.
Early reviews are nice, but they're kind of a moot point. Cataclysm got 95% out the starting gate in many reviews, but the expansion saw subs at their lowest since BC, finished driving the wedge between the hardcore and casual player bases that Wrath began, and ended up ultimately as a failed experiment wherein Blizz tried to push the player base into a more hardcore mindset with harder release and 4.1 5-mans, 10/25-man content being normalized to 25-man difficulty (when before, 10-man was easier to account for a smaller margin of error with only 10 people), and it blew up in their faces. They went back to ICC's Frozen Halls difficulty level with the Hour of Twilight 5-mans, and LFR opened up raiding to a portion of the player base that had historically not raided (skyrocketing raid attendance), and while that stemmed the sub bleed for one quarter, it was too little too long and Dragon Soul had to stretch longer than it was built to.