Former France midfielder Diarra spent an unhappy two years at Upton Park, making just 14 appearances before he was released in the summer.
The 33-year-old joined Charlton in February and has just agreed a new contract until the summer of 2016.
He told the club’s matchday programme: “My first experience in England was frustrating because I didn’t play many games at West Ham.
“I did well in training but it just wasn’t football. They played a lot of long balls but for me that is too easy. I’ve always played hard stuff. I like to get into position with pressure.
“If you are not first choice with the manager you have to wait for injuries or suspensions to get your chance and even then I didn’t get it. But that’s in the past for me now.
“I didn’t learn anything during my two years at West Ham. I’ve learned more in the last month at Charlton because we try to play football. We try to keep possession and win every game and for me that is football.
“It’s about ambition. I’m a competitive guy and I need to win every game, not only some games.”