I think that some people, in their non-constructive criticism of him over the past few years simply did not see the bigger picture. Yes, he has been poor but I, personally always saw a good player and a passionate player who just wants to play football for Everton.
1: Bad managers: This cannot be doubted. He seemed to be shoe horned in and never really given a specific role during a game. These managers just didn't know how to develop him or where to play him.
2: He was 18/19 when he came in, as some have mentioned, there is no idea of how good or bad a player is going to be throughout his career, at that age (apart from the freaks of nature like Rooney). A lot of pressure to try to be the main man was given to him by fans and when it didn't look like he was going to be the player he seemed, after one wonder goal, then the boo boys turned on him, and turned quickly, and at times very harshly as well. As a young player this is going to affect your confidence.
3: The players he played with, along with point one, did not give him the best opportunity to show what he has to offer, too many times he has been let down by the system or the fact that other players were not letting him develop. I think this is being shown this season and is very obvious to see, a manager comes in and sees how exactly to develop him, where to play him and who to play him with (when available).
4: Too much exposure: Again with the bad managers note, he was simply played too much. He wasn't ready for that amount of games at this level, he should probably gone on loan to get games or continue to be rotated/come off the bench.
I am certainly not saying he is 'boss again', because he has never been 'boss' but he had something about him and for the last few years he has been poor to decent. This season he has been decent to good, the last couple of games he has been great against very good midfield opponents. There is an obvious upward curve on his progression this season, under Ancelotti I only expect that to keep on rising.