if you see the comments, Chelsea fans loooooove defending Mikel and pretending he's a "stopper" and that he single handedly stopped Barcelona and Munich in the Champions league two years ago.
but somehow this is a player not good enough to keep David Luiz from challenging for his holding role and the club had to spend 21 million pounds on a Serbian dude to replace him.
i have a tendency to overstate his deficiencies because i don't like him as a player. he's certainly not bad. he completes a very high percentage of his passes (over 90% in 2011-2012), makes a couple tackles per game, has a decent range of passing, makes interceptions and knows his role. he's just not an elite defensive midfielder, which is what a title challenging EPL side would want if they are consistently playing in that style. he's also not an all-rounder and seems unable to provide any attacking impetus in games where he is directed to play the holding role. i don't think he can hang his hat on his defensive duties given that he lacks anything special in his distribution and goal scoring.