He is not a world class player by any means and never has been. However, he has merited a place in the team for most of his career.
He started out as a talented off-spinner at a time when Saqlain was on the decline due to over-dependency on the doosra. In addition, he was also a much better batsman. In the Woolmer era that followed, he evolved into one our best middle-order batsman and has been a top fielder throughout his career.
He was woeful from 2010 to 2014, and he was largely out of the team in this period. Did not play in two World Cups and was completely shunted for a couple of years. However, since 2015, he has been one of our most prolific players.
He has his weaknesses. He is an average player of fast bowling which is why he has never excelled against pace-heavy teams, but he is relatively one of our best players. Nonetheless, he is too old now and should probably be moved on.