Before we begin, I want to note that there is a difference between most disappointing and just plain worst. The players below are generally a mix of the two. Just playing bad won't get you this list and just being purely disappointing will not either. A combination of the two is necessary. At least that's what I'm thinking in my head.
5. Ross Barkley
This is probably the only shock addition to this list. Barkley is definitely more along the lines of disappointing than purely bad. People (me) just seemed to think that this was the year that Barkley would take the huge leap forward and turn into that great player we expect him to be in the future. But in all fairness, he is still extremely young and still learning top flight football. But his loan spells (especially to Leeds United) were quite disappointing and it was even more disappointing to see him play for Everton. He seemed to make the same mistakes he made last year with much less improvement than most (I) hoped. He still lost possession at silly times when we had momentum and would often disappear in matches.
Barkley still has shown flashes of greatness and can easily turn it around next year. Let's hope his great leap forward comes soon.
4. Steven Naismith
Steven Naismith should probably be higher up on this list but the people above him were so bad that he slipped down to fourth. Naismith was just plain aggravating to watch. He came in at the beginning of the season with a lot of hype since he had already partnered well with Jelavic at Rangers. It seemed he wouldn't need too much time to mesh well with the squad. But honestly, that was the least of his worries. The quality just wasn't there. He lost the ball to often and just couldn't beat defenders. It seemed as if he couldn't jump up to the English game.
Naismith did score some crucial goals though, and you can't really question his motor. He did at the end of the season also admit his form was quite poor during the whole season. These are all good signs that may point to a better future but I remain skeptical. Naismith seems like a good guy and I really do hope he can turn it around next season.
3. Phil Neville
I will keep it short with Neville because we all know his deficiencies. It just looked like he retired one season too late. He was one step behind everywhere and was a direct cause to a few goals and just looked outclassed in almost every situation. He had a great career and he will one day become a pretty good coach too. His playing career was just one season too long.
2. Nikica Jelavic
Many could argue that Jelavic should be number one. He came in with sky high expectations. He had already proven that he could score at this level and he seemed to be the player needed to put Everton over the hump and get to the Champions League or bring us an FA Cup. None of this happened and Jelavic was just plain awful for almost all of the season. Jelavic missed even easy open goals and seemed to get pushed around too much by defenders. His lack of confidence then snowballed into worse performances and by the end of the season he didn't even get too much playing time.
We could call this the sophomore slump. We could also just call this just a regular season long slump that all players have. I think he will regain his form at some point and start scoring goals, maybe not at the rate he was scoring last season, but definitely back to a solidly contributing striker. Because we really, really need him.
Oh how the mighty have fallen. Heitinga, who was a solid, strong, physical defender, was never spectacular in his defending but always got the job done. After a great season last year, we expected him to be the reliable and versatile player he is. Well, the exact opposite happened. He was directly responsible for multiple losses. Worse, his form didn't seem to get any better at any point. He seemed to get manhandled by puny strikers. His strongest trait ended up being his biggest flaw last season.
To be honest, Heitinga probably needs a change of scenery. I don't know if he will get it, but he really needs a new club and I know he has the skill set to excel there. But at Everton, he just isn't going to break into a starting job with the sort of unreliability he has shown and he just plain too expensive to keep on our books.