Just a completely overrated player in the first instance. We constantly got told it's our fault, he was great at Juventus and France. Even though he was probably never "great", just a useful talent to have if compensated for. Being associated with great sides or putting in the odd excellent performance does that equal greatness. Great players don't need that everything lined up perfectly, they produce without excuses.
Then you had the people saying the manager has to motivate the player, or the ones that simply denied that he didn't work hard. Even though it was right before our eyes every game. The last few months and Pogba's unprofessional attitude should make it clearer for them. Hard work is part of being great.
Then you have the people that said he can do everything as a midfielder. Maybe he can, once in a blue moon, or across a string of games. But unfortunately never in a way that made a difference. It's far more useful to have a midfielder that understands positional play and passes consistently than one who can play 50 yard passes with the outside of his right boot, then nothing. The consistency of the elements of his game that make up a central midfielder are appalling.
Then there was his agent. Not his fault apparently. Despite the fact that most people are perfectly capable of realising that a man that speaks for you in public represents you. If he remains in that position, the implication is his statements represent your own feelings. In addition to his failings on the pitch, which would otherwise be frustrating but not a death knell for his reputation, this made him thoroughly unlikeable.